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Quantum Hall Effect in Electron-Doped Black Phosphorus Field-Effect Transistors
Authors:
Fangyuan Yang,
Zuocheng Zhang,
Nai Zhou Wang,
Guo Jun Ye,
Wenkai Lou,
Xiaoying Zhou,
Kenji Watanabe,
Takashi Taniguchi,
Kai Chang,
Xian Hui Chen,
Yuanbo Zhang
Abstract:
The advent of black phosphorus field-effect transistors (FETs) has brought new possibilities in the study of two-dimensional (2D) electron systems. In a black phosphorus FET, the gate induces highly anisotropic 2D electron and hole gases. Although the 2D hole gas in black phosphorus has reached high carrier mobilities that led to the observation of the integer quantum Hall effect, the improvement…
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The advent of black phosphorus field-effect transistors (FETs) has brought new possibilities in the study of two-dimensional (2D) electron systems. In a black phosphorus FET, the gate induces highly anisotropic 2D electron and hole gases. Although the 2D hole gas in black phosphorus has reached high carrier mobilities that led to the observation of the integer quantum Hall effect, the improvement in the sample quality of the 2D electron gas (2DEG) has however been only moderate; quantum Hall effect remained elusive. Here, we obtain high quality black phosphorus 2DEG by defining the 2DEG region with a prepatterned graphite local gate. The graphite local gate screens the impurity potential in the 2DEG. More importantly, it electrostatically defines the edge of the 2DEG, which facilitates the formation of well-defined edge channels in the quantum Hall regime. The improvements enable us to observe precisely quantized Hall plateaus in electron-doped black phosphorus FET. Magneto-transport measurements under high magnetic fields further revealed a large effective mass and an enhanced Landé g-factor, which points to strong electron-electron interaction in black phosphorus 2DEG. Such strong interaction may lead to exotic many-body quantum states in the fractional quantum Hall regime.
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Submitted 20 September, 2018;
originally announced September 2018.
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Resolving and Tuning Mechanical Anisotropy in Black Phosphorus via Nanomechanical Multimode Resonance Spectromicroscopy
Authors:
Zenghui Wang,
Hao Jia,
Xu-Qian Zheng,
Rui Yang,
G. J. Ye,
X. H. Chen,
Philip X. -L. Feng
Abstract:
Black phosphorus (P) has emerged as a layered semiconductor with a unique crystal structure featuring corrugated atomic layers and strong in-plane anisotropy in its physical properties. Here, we demonstrate that the crystal orientation and mechanical anisotropy in free-standing black P thin layers can be precisely determined by spatially resolved multimode nanomechanical resonances. This offers a…
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Black phosphorus (P) has emerged as a layered semiconductor with a unique crystal structure featuring corrugated atomic layers and strong in-plane anisotropy in its physical properties. Here, we demonstrate that the crystal orientation and mechanical anisotropy in free-standing black P thin layers can be precisely determined by spatially resolved multimode nanomechanical resonances. This offers a new means for resolving important crystal orientation and anisotropy in black P device platforms in situ beyond conventional optical and electrical calibration techniques. Furthermore, we show that electrostatic-gating-induced straining can continuously tune the mechanical anisotropic effects on multimode resonances in black P electromechanical devices. Combined with finite element modeling (FEM), we also determine the Young's moduli of multilayer black P to be 116.1 and 46.5 GPa in the zigzag and armchair directions, respectively.
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Submitted 25 September, 2016;
originally announced September 2016.
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Evolution of high-temperature superconductivity from low-Tc phase tuned by carrier concentration in FeSe thin flakes
Authors:
B. Lei,
J. H. Cui,
Z. J. Xiang,
C. Shang,
N. Z. Wang,
G. J. Ye,
X. G. Luo,
T. Wu,
Z. Sun,
X. H. Chen
Abstract:
In contrast to bulk FeSe superconductor, heavily electron-doped FeSe-derived superconductors show relatively high Tc without hole Fermi surfaces and nodal superconducting gap structure, which pose great challenges on pairing theories in the iron-based superconductors. In the heavily electron-doped FeSe-based superconductors, the dominant factors and the exact working mechanism that is responsible…
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In contrast to bulk FeSe superconductor, heavily electron-doped FeSe-derived superconductors show relatively high Tc without hole Fermi surfaces and nodal superconducting gap structure, which pose great challenges on pairing theories in the iron-based superconductors. In the heavily electron-doped FeSe-based superconductors, the dominant factors and the exact working mechanism that is responsible for the high Tc need to be clarified. In particular, a clean control of carrier concentration remains to be a challenge for revealing how superconductivity and Fermi surface topology evolves with carrier concentration in bulk FeSe. Here, we report the evolution of superconductivity in the FeSe thin flake with systematically regulated carrier concentrations by liquid-gating technique. High-temperature superconductivity at 48 K can be achieved only with electron doping tuned by gate voltage in FeSe thin flake with Tc less than 10 K. This is the first time to achieve such a high temperature superconductivity in FeSe without either epitaxial interface or external pressure. It definitely proves that the simple electron-doping process is able to induce high-temperature superconductivity with Tc as high as 48 K in bulk FeSe. Intriguingly, our data also indicates that the superconductivity is suddenly changed from low-Tc phase to high-Tc phase with a Lifshitz transition at certain carrier concentration. These results help us to build a unified picture to understand the high-temperature superconductivity among all FeSe-derived superconductors and shed light on further pursuit of higher Tc in these materials.
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Submitted 2 September, 2015;
originally announced September 2015.
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Quantum Hall Effect in Black Phosphorus Two-dimensional Electron Gas
Authors:
Likai Li,
Fangyuan Yang,
Guo Jun Ye,
Zuocheng Zhang,
Zengwei Zhu,
Wen-Kai Lou,
Liang Li,
Kenji Watanabe,
Takashi Taniguchi,
Kai Chang,
Yayu Wang,
Xian Hui Chen,
Yuanbo Zhang
Abstract:
Development of new, high quality functional materials has been at the forefront of condensed matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the material base of two-dimensional electron systems. Significant progress has been made to achieve high mobility black phosphorus two-dimensional electron gas (2DEG) since the development of the first black phosph…
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Development of new, high quality functional materials has been at the forefront of condensed matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the material base of two-dimensional electron systems. Significant progress has been made to achieve high mobility black phosphorus two-dimensional electron gas (2DEG) since the development of the first black phosphorus field-effect transistors (FETs)$^{1-4}$. Here, we reach a milestone in developing high quality black phosphorus 2DEG - the observation of integer quantum Hall (QH) effect. We achieve high quality by embedding the black phosphorus 2DEG in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DEG, and brings the carrier Hall mobility up to 6000 $cm^{2}V^{-1}s^{-1}$. The exceptional mobility enabled us, for the first time, to observe QH effect, and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime.
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Submitted 19 May, 2015; v1 submitted 27 April, 2015;
originally announced April 2015.
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Black Phosphorus Nanoelectromechanical Resonators Vibrating at Very High Frequencies
Authors:
Zenghui Wang,
Hao Jia,
Xuqian Zheng,
Rui Yang,
Zefang Wang,
G. J. Ye,
X. H. Chen,
Jie Shan,
Philip X. -L. Feng
Abstract:
We report on experimental demonstration of a new type of nanoelectromechanical resonators based on black phosphorus crystals. Facilitated by a highly efficient dry transfer technique, crystalline black phosphorus flakes are harnessed to enable drumhead resonators vibrating at high and very high frequencies (HF and VHF bands, up to ~100MHz). We investigate the resonant vibrational responses from th…
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We report on experimental demonstration of a new type of nanoelectromechanical resonators based on black phosphorus crystals. Facilitated by a highly efficient dry transfer technique, crystalline black phosphorus flakes are harnessed to enable drumhead resonators vibrating at high and very high frequencies (HF and VHF bands, up to ~100MHz). We investigate the resonant vibrational responses from the black phosphorus crystals by devising both electrical and optical excitation schemes, in addition to measuring the undriven thermomechanical motions in these suspended nanostructures. Flakes with thicknesses from ~200nm down to ~20nm clearly exhibit elastic characteristics transitioning from the plate to the membrane regime. Both frequency- and time-domain measurements of the nanomechanical resonances show that very thin black phosphorus crystals hold interesting promises for moveable and vibratory devices, and for semiconductor transducers where high-speed mechanical motions could be coupled to the attractive electronic and optoelectronic properties of black phosphorus.
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Submitted 4 April, 2015;
originally announced April 2015.
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Pressure-induced Lifshitz transition in black phosphorus
Authors:
Z. J. Xiang,
G. J. Ye,
C. Shang,
B. Lei,
N. Z. Wang,
K. S. Yang,
D. Y. Liu,
F. B. Meng,
X. G. Luo,
L. J. Zou,
Z. Sun,
Y. B. Zhang,
X. H. Chen
Abstract:
In a semimetal, both electron and hole carriers contribute to the density of states at the Fermi level. The small band overlaps and multi-band effects give rise to many novel electronic properties, such as relativistic Dirac fermions with linear dispersion, titanic magnetoresistance and unconventional superconductivity. Black phosphorus has recently emerged as an exceptional semiconductor with hig…
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In a semimetal, both electron and hole carriers contribute to the density of states at the Fermi level. The small band overlaps and multi-band effects give rise to many novel electronic properties, such as relativistic Dirac fermions with linear dispersion, titanic magnetoresistance and unconventional superconductivity. Black phosphorus has recently emerged as an exceptional semiconductor with high carrier mobility and a direct, tunable bandgap. Of particular importance is the search for exotic electronic states in black phosphorus, which may amplify the material's potential beyond semiconductor devices. Here we show that a moderate hydrostatic pressure effectively suppresses the band gap and induces a Lifshitz transition from semiconductor to semimetal in black phosphorus; a colossal magnetoresistance is observed in the semimetallic phase. Quantum oscillations in high magnetic field reveal the complex Fermi surface topology of the semimetallic black phosphorus. In particular, a Dirac-like fermion emerges at around 1.2 GPa, which is continuously tuned by external pressure. The observed semi-metallic behavior greatly enriches black phosphorus's material property, and sets the stage for the exploration of novel electronic states in this material. Moreover, these interesting behaviors make phosphorene a good candidate for the realization of a new two-dimensional relativistic electron system, other than graphene.
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Submitted 4 December, 2015; v1 submitted 1 April, 2015;
originally announced April 2015.
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Quantum Oscillations in Black Phosphorus Two-dimensional Electron Gas
Authors:
Likai Li,
Guo Jun Ye,
Vy Tran,
Ruixiang Fei,
Guorui Chen,
Huichao Wang,
Jian Wang,
Kenji Watanabe,
Takashi Taniguchi,
Li Yang,
Xian Hui Chen,
Yuanbo Zhang
Abstract:
Two-dimensional electron gases (2DEG) have been an important source of experimental discovery and conceptual development in condensed matter physics for decades. When combined with the unique electronic properties of two-dimensional (2D) crystals, rich new physical phenomena can be probed at the quantum level. Here, we create a new 2DEG in black phosphorus, a recent member of the two-dimensional a…
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Two-dimensional electron gases (2DEG) have been an important source of experimental discovery and conceptual development in condensed matter physics for decades. When combined with the unique electronic properties of two-dimensional (2D) crystals, rich new physical phenomena can be probed at the quantum level. Here, we create a new 2DEG in black phosphorus, a recent member of the two-dimensional atomic crystal family, using a gate electric field. We achieve high carrier mobility in black phosphorus 2DEG by placing it on a hexagonal boron nitride substrate (h-BN). This allows us, for the first time, to observe quantum oscillations in this material. The temperature and magnetic field dependence of the oscillations yields crucial information about the system, such as cyclotron mass and lifetime of its charge carriers. Our results, coupled with the fact that black phosphorus possesses anisotropic energy bands with a tunable, direct bandgap, distinguishes black phosphorus 2DEG as a novel system with unique electronic and optoelectronic properties.
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Submitted 24 November, 2014;
originally announced November 2014.
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Black phosphorus field-effect transistors
Authors:
Likai Li,
Yijun Yu,
Guo Jun Ye,
Qingqin Ge,
Xuedong Ou,
Hua Wu,
Donglai Feng,
Xian Hui Chen,
Yuanbo Zhang
Abstract:
Two-dimensional crystals have emerged as a new class of materials with novel properties that may impact future technologies. Experimentally identifying and characterizing new functional two-dimensional materials in the vast material pool is a tremendous challenge, and at the same time potentially rewarding. In this work, we succeed in fabricating field-effect transistors based on few-layer black p…
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Two-dimensional crystals have emerged as a new class of materials with novel properties that may impact future technologies. Experimentally identifying and characterizing new functional two-dimensional materials in the vast material pool is a tremendous challenge, and at the same time potentially rewarding. In this work, we succeed in fabricating field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometers. Drain current modulation on the order of 10E5 is achieved in samples thinner than 7.5 nm at room temperature, with well-developed current saturation in the IV characteristics, both are important for reliable transistor performance of the device. Sample mobility is also found to be thickness dependent, with the highest value up to ~ 1000 cm2/Vs obtained at thickness ~ 10 nm. Our results demonstrate the potential of black phosphorus thin crystal as a new two-dimensional material for future applications in nano-electronic devices.
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Submitted 16 January, 2014;
originally announced January 2014.
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Phase diagram and physical properties of NaFe$_{1-x}$Cu$_x$As single crystals
Authors:
A. F. Wang,
J. J. Lin,
P. Cheng,
G. J. Ye,
F. Chen,
J. Q. Ma,
X. F. Lu,
B. Lei,
X. G. Luo,
X. H. Chen
Abstract:
A series of high quality NaFe$_{1-x}$Cu$_x$As single crystals has been grown by a self-flux technique, which were systematically characterized via structural, transport, thermodynamic, and high pressure measurements. Both the structural and magnetic transitions are suppressed by Cu doping, and bulk superconductivity is induced by Cu doping. Superconducting transition temperature ($T_c$) is initial…
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A series of high quality NaFe$_{1-x}$Cu$_x$As single crystals has been grown by a self-flux technique, which were systematically characterized via structural, transport, thermodynamic, and high pressure measurements. Both the structural and magnetic transitions are suppressed by Cu doping, and bulk superconductivity is induced by Cu doping. Superconducting transition temperature ($T_c$) is initially enhanced from 9.6 to 11.5 K by Cu doping, and then suppressed with further doping. A phase diagram similar to NaFe$_{1-x}$Co$_x$As is obtained except that insulating instead of metallic behavior is observed in extremely overdoped samples. $T_c$'s of underdoped, optimally doped, and overdoped samples are all notably enhanced by applying pressure. Although a universal maximum transition temperature ($T_c^{max}$) of about 31 K under external pressure is observed in underdoped and optimally doped NaFe$_{1-x}$Co$_x$As, $T_c^{max}$ of NaFe$_{1-x}$Cu$_x$As is monotonously suppressed by Cu doping, suggesting that impurity potential of Cu is stronger than Co in NaFeAs. The comparison between Cu and Co doping effect in NaFeAs indicates that Cu serves as an effective electron dopant with strong impurity potential, but part of the doped electrons are localized and do not fill the energy bands as predicted by the rigid-band model.
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Submitted 23 July, 2013;
originally announced July 2013.
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Calorimetric study in single crystal of CsFe$_2$As$_2$
Authors:
A. F. Wang,
B. Y. Pan,
X. G. Luo,
F. Chen,
Y. J. Yan,
J. J. Ying,
G. J. Ye,
P. Cheng,
X. C. Hong,
S. Y. Li,
X. H. Chen
Abstract:
We measured resistivity and specific heat of high-quality CsFe$_2$As$_2$ single crystals, which were grown by using a self-flux method. The CsFe$_2$As$_2$ crystal shows sharp superconducting transition at 1.8 K with the transition width of 0.1 K. The sharp superconducting transition and pronounced jump in specific heat indicate high quality of the crystals. Analysis on the superconducting-state sp…
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We measured resistivity and specific heat of high-quality CsFe$_2$As$_2$ single crystals, which were grown by using a self-flux method. The CsFe$_2$As$_2$ crystal shows sharp superconducting transition at 1.8 K with the transition width of 0.1 K. The sharp superconducting transition and pronounced jump in specific heat indicate high quality of the crystals. Analysis on the superconducting-state specific heat supports unconventional pairing symmetry in CsFe$_2$As$_2$.
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Submitted 22 February, 2013;
originally announced February 2013.
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Power-law Temperature Dependent Hall Angle in the Normal State and its Correlation with Superconductivity in iron-pnictides
Authors:
Y. J. Yan,
A. F. Wang,
X. G. Luo,
Z. Sun,
J. J. Ying,
G. J. Ye,
P. Chen,
J. Q. Ma,
X. H. Chen
Abstract:
We report Hall measurement of the normal state in K- and Co-doped BaFe$_2$As$_2$, as well NaFe$_{1-x}$Co$_x$As. We found that a power-law temperature dependence of Hall angle, cot$θ_{\rm H}$$\propto$ $T^β$, prevails in normal state with temperature range well above the structural, spin-density-wave and superconducting transitions for the all samples with various doping levels. The power $β$ is nea…
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We report Hall measurement of the normal state in K- and Co-doped BaFe$_2$As$_2$, as well NaFe$_{1-x}$Co$_x$As. We found that a power-law temperature dependence of Hall angle, cot$θ_{\rm H}$$\propto$ $T^β$, prevails in normal state with temperature range well above the structural, spin-density-wave and superconducting transitions for the all samples with various doping levels. The power $β$ is nearly 4 for the parent compounds and the heavily underdoped samples, while around 3 for the superconducting samples. The $β$ suddenly changes from 4 to 3 at a doping level that is close to the emergence of superconductivity. It suggests that the $β$ of $\sim 3$ is clearly tied to the superconductivity. Our data suggest that, similar to cuprates, there exists a connection between the physics in the normal state and superconductivity of iron-pnictides. These findings shed light on the mechanism of high-temperature superconductivity.
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Submitted 8 January, 2013;
originally announced January 2013.
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Physical properties in hole-doped SrFe$_{2-x}$Cu$_x$As$_2$ single crystals
Authors:
Y. J. Yan,
P. Cheng,
J. J. Ying,
X. G. Luo,
F. Chen,
H. Y. Zou,
A. F. Wang,
G. J. Ye,
Z. J. Xiang,
J. Q. Ma,
X. H. Chen
Abstract:
We report the structural, magnetic and electronic transport properties of SrFe$_{2-x}$Cu$_x$As$_2$ single crystals grown by self-flux technique. SrCu$_2$As$_2$ and SrFe$_2$As$_2$ both crystallize in ThCr$_2$Si$_2$-type (122-type) structure at room temperature, but exhibit distinct magnetic and electronic transport properties. The x-ray photoelectron spectroscopy(XPS) Cu-2p core line position, resi…
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We report the structural, magnetic and electronic transport properties of SrFe$_{2-x}$Cu$_x$As$_2$ single crystals grown by self-flux technique. SrCu$_2$As$_2$ and SrFe$_2$As$_2$ both crystallize in ThCr$_2$Si$_2$-type (122-type) structure at room temperature, but exhibit distinct magnetic and electronic transport properties. The x-ray photoelectron spectroscopy(XPS) Cu-2p core line position, resistivity, susceptibility and positive Hall coefficient indicate that SrCu$_2$As$_2$ is an sp-band metal with Cu in the 3d$^{10}$ electronic configuration corresponding to the valence state Cu$^{1+}$. The almost unchanged Cu-2p core line position in SrFe$_{2-x}$Cu$_x$As$_2$ compared with SrCu$_2$As$_2$ indicates that partial Cu substitutions for Fe in SrFe$_2$As$_2$ may result in hole doping rather than the expected electron doping. No superconductivity is induced by Cu substitution on Fe sites, even though the structural/spin density wave(SDW) transition is gradually suppressed with increasing Cu doping.
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Submitted 3 December, 2012;
originally announced December 2012.
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Pressure effects on superconducting properties of single-crystalline Co doped NaFeAs
Authors:
A. F. Wang,
Z. J. Xiang,
J. J. Ying,
Y. J. Yan,
P. Cheng,
G. J. Ye,
X. G. Luo,
X. H. Chen
Abstract:
Resistivity and magnetic susceptibility measurements under external pressure were performed on single-crystals NaFe1-xCoxAs (x=0, 0.01, 0.028, 0.075, 0.109). The maximum Tc enhanced by pressure in both underdoped and optimally doped NaFe1-xCoxAs is the same, as high as 31 K. The overdoped sample with x = 0.075 also shows a positive pressure effect on Tc, and an enhancement of Tc by 13 K is achieve…
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Resistivity and magnetic susceptibility measurements under external pressure were performed on single-crystals NaFe1-xCoxAs (x=0, 0.01, 0.028, 0.075, 0.109). The maximum Tc enhanced by pressure in both underdoped and optimally doped NaFe1-xCoxAs is the same, as high as 31 K. The overdoped sample with x = 0.075 also shows a positive pressure effect on Tc, and an enhancement of Tc by 13 K is achieved under pressure of 2.3 GPa. All the superconducting samples show large positive pressure coefficient on superconductivity, being different from Ba(Fe1-xCox)2As2. However, the superconductivity cannot be induced by pressure in heavily overdoped non-superconducting NaFe0.891Co0.109As. These results provide evidence for that the electronic structure is much different between superconducting and heavily overdoped non-superconducting NaFe1-xCoxAs, being consistent with the observation by angle-resolved photoemission spectroscopy.
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Submitted 23 July, 2012;
originally announced July 2012.
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A crossover in phase diagram of NaFe$_{1-x}$Co$_x$As determined by electronic transport measurements
Authors:
A. F. Wang,
J. J. Ying,
X. G. Luo,
Y. J. Yan,
D. Y. Liu,
Z. J. Xiang,
P. Cheng,
G. J. Ye,
L. J. Zou,
Z. Sun,
X. H. Chen
Abstract:
We report electronic transport measurements on single crystals of NaFe$_{1-x}$Co$_x$As system. We found that the cotangent of Hall angle, cot$θ_{\rm H}$, follows $T^4$ for the parent compound with filamentary superconductivity and $T^2$ for the heavily-overdoped non-superconducting sample. While it exhibits approximately $T^3$-dependence in all the superconducting samples, suggesting this behaivor…
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We report electronic transport measurements on single crystals of NaFe$_{1-x}$Co$_x$As system. We found that the cotangent of Hall angle, cot$θ_{\rm H}$, follows $T^4$ for the parent compound with filamentary superconductivity and $T^2$ for the heavily-overdoped non-superconducting sample. While it exhibits approximately $T^3$-dependence in all the superconducting samples, suggesting this behaivor is associated with bulk superconductivity in ferropnictides. A deviation develops below a characteristic temperature $T^*$ well above the structural and superconducting transitions, accompanied by a departure from power-law temperature dependence in resistivity. The doping dependence of $T^*$ resembles the crossover line of pseudogap phase in cuprates.
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Submitted 11 December, 2012; v1 submitted 16 July, 2012;
originally announced July 2012.
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Anomalous impurity effects in the iron-based superconductor KFe$_2$As$_2$
Authors:
A. F. Wang,
S. Y. Zhou,
X. G. Luo,
X. C. Hong,
Y. J. Yan,
J. J. Ying,
P. Cheng,
G. J. Ye,
Z. J. Xiang,
S. Y. Li,
X. H. Chen
Abstract:
High-quality K(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals have been grown by using KAs flux method. Instead of increasing the superconducting transition temperature $T_{\rm c}$ through electron doping, we find that Co impurities rapidly suppress $T_{\rm c}$ down to zero at only $x \approx$ 0.04. Such an effective suppression of $T_{\rm c}$ by impurities is quite different from that observed in Ba…
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High-quality K(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals have been grown by using KAs flux method. Instead of increasing the superconducting transition temperature $T_{\rm c}$ through electron doping, we find that Co impurities rapidly suppress $T_{\rm c}$ down to zero at only $x \approx$ 0.04. Such an effective suppression of $T_{\rm c}$ by impurities is quite different from that observed in Ba$_{0.5}$K$_{0.5}$Fe$_2$As$_2$ with multiple nodeless superconducting gaps. Thermal conductivity measurements in zero field show that the residual linear term $κ_0/T$ only change slightly with $3.4\%$ Co doping, despite the sharp increase of scattering rate. The implications of these anomalous impurity effects are discussed.
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Submitted 21 January, 2014; v1 submitted 10 June, 2012;
originally announced June 2012.
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Phase Diagram and Calorimetric Properties of NaFe$_{1-x}$Co$_x$As
Authors:
A. F. Wang,
X. G. Luo,
Y. J. Yan,
J. J. Ying,
Z. J. Xiang,
G. J. Ye,
P. Cheng,
Z. Y. Li,
W. J. Hu,
X. H. Chen
Abstract:
We measured the resistivity and magnetic susceptibility to map out the phase diagram of single crystalline NaFe$_{1-x}$Co$_x$As. Replacement of Fe by Co suppresses both the structural and magnetic transition, while enhances the superconducting transition temperature ($T_{\rm c}$) and superconducting component fraction. Magnetic susceptibility exhibits temperature-linear dependence in the high temp…
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We measured the resistivity and magnetic susceptibility to map out the phase diagram of single crystalline NaFe$_{1-x}$Co$_x$As. Replacement of Fe by Co suppresses both the structural and magnetic transition, while enhances the superconducting transition temperature ($T_{\rm c}$) and superconducting component fraction. Magnetic susceptibility exhibits temperature-linear dependence in the high temperatures up to 500 K for all the superconducting samples, but such behavior suddenly breaks down for the non-superconducting overdoped crystal, suggesting that the superconductivity is closely related to the T-linear dependence of susceptibility. Analysis on the superconducting-state specific heat for the optimally doped crystal provides strong evidence for a two-band s-wave order parameter with gap amplitudes of $Δ_1(0)/k_{\rm B}T_{\rm c}$= 1.78 and $Δ_2(0)/k_{\rm B}T_{\rm c}$=3.11, being consistent with the nodeless gap symmetry revealed by angle-resolved photoemission spectroscopy experiment.
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Submitted 21 April, 2012; v1 submitted 16 April, 2012;
originally announced April 2012.
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Metamagnetic transition in Ca$_{1-x}$Sr$_x$Co$_2$As$_2$($x$ = 0 and 0.1) single crystals
Authors:
J. J. Ying,
Y. J. Yan,
A. F. Wang,
Z. J. Xiang,
P. Cheng,
G. J. Ye,
X. H. Chen
Abstract:
We report the magnetism and transport measurements of CaCo$_2$As$_2$ and Ca$_{0.9}$Sr$_{0.1}$Co$_2$As$_2$ single crystals. Antiferromagnetic transition was observed at about 70 K and 90 K for CaCo$_2$As$_2$ and Ca$_{0.9}$Sr$_{0.1}$Co$_2$As$_2$, respectively. Magnetism and magnetoresistance measurements reveal metamagnetic transition from an antiferromagnetic state to a ferromagnetic state with the…
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We report the magnetism and transport measurements of CaCo$_2$As$_2$ and Ca$_{0.9}$Sr$_{0.1}$Co$_2$As$_2$ single crystals. Antiferromagnetic transition was observed at about 70 K and 90 K for CaCo$_2$As$_2$ and Ca$_{0.9}$Sr$_{0.1}$Co$_2$As$_2$, respectively. Magnetism and magnetoresistance measurements reveal metamagnetic transition from an antiferromagnetic state to a ferromagnetic state with the critical field of 3.5 T and 1.5 T respectively along c-axis for these two materials at low temperature. For the field along ab-plane, spins can also be fully polarized above the field of 4.5 T for Ca$_{0.9}$Sr$_{0.1}$Co$_2$As$_2$. While for CaCo$_2$As$_2$, spins can not be fully polarized up to 7 T. We proposed the cobalt moments of these two materials should be ordered ferromagnetically within the ab-plane but antiferromagnetically along the c-axis(A-type AFM).
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Submitted 8 April, 2012;
originally announced April 2012.
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Enhanced Superconductivity by Rare-earth Metal-doping in Phenanthrene
Authors:
X. F. Wang,
X. G. Luo,
J. J. Ying,
Z. J. Xiang,
S. L. Zhang,
R. R. Zhang,
Y. H. Zhang,
Y. J. Yan,
A. F. Wang,
P. Cheng,
G. J. Ye,
X. H. Chen
Abstract:
We successfully synthesized La- and Sm-doped phenanthrene powder samples and discovered superconductivity at $T_{\rm c}$ around 6 K in them. The $T_{\rm c}$s are 6.1 K for LaPhenanthrene and 6.0 K for SmPhenanthrene, which are enhanced by about 1 K and 0.5 K compared to those in $A_3$Phenanthrene ($A$=K and Rb) and in $Ae_{1.5}$Phenanthrene ($Ae$ = Sr and Ba) superconductors respectively. The supe…
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We successfully synthesized La- and Sm-doped phenanthrene powder samples and discovered superconductivity at $T_{\rm c}$ around 6 K in them. The $T_{\rm c}$s are 6.1 K for LaPhenanthrene and 6.0 K for SmPhenanthrene, which are enhanced by about 1 K and 0.5 K compared to those in $A_3$Phenanthrene ($A$=K and Rb) and in $Ae_{1.5}$Phenanthrene ($Ae$ = Sr and Ba) superconductors respectively. The superconductive shielding fractions for LaPhenanthrene and SmPhenanthrene are 46.1%$ and 49.8$%$ at 2 K, respectively. The little effect of the doping of the magnetic ion Sm$^{3+}$ on $T_c$ and the positive pressure dependence coefficient on $T_{\rm c}$ strongly suggests unconventional superconductivity in the doped phenanthrene superconductors. The charge transfer to organic molecules from dopants of La and Sm induces a redshift of 7 cm$^{-1}$ per electron for the mode at 1441 cm$^{-1}$ in the Raman spectra, which is almost the same as those observed in $A_3$Phenanthrene ($A$=K and Rb) and $Ae_{1.5}$Phenanthrene ($Ae$ = Sr and Ba) superconductors.
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Submitted 27 March, 2012;
originally announced March 2012.
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Transport Properties and Electronic Phase Diagram of Single-Crystalline Ca$_{10}$(Pt$_3$As$_8$) ((Fe$_{1-x}$Pt$_x$)$_2$As$_2$)$_5$
Authors:
Z. J. Xiang,
X. G. Luo,
J. J. Ying,
X. F. Wang,
Y. J. Yan,
A. F. Wang,
P. Cheng,
G. J. Ye,
X. H. Chen
Abstract:
Sizable single-crystalline samples of Ca$_{10}$(Pt$_3$As$_8$)((Fe$_{1-x}$Pt$_x$)$_2$As$_2$)$_5$ (the 10-3-8 phase) with 0$\leq x<$0.1 have been grown and systematically characterized via X-Ray diffraction, magnetic, and transport measurements. The undoped sample is a heavily doped semiconductor with no sign of magnetic order down to 2 K. With increasing Pt content, the metallic behavior appears an…
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Sizable single-crystalline samples of Ca$_{10}$(Pt$_3$As$_8$)((Fe$_{1-x}$Pt$_x$)$_2$As$_2$)$_5$ (the 10-3-8 phase) with 0$\leq x<$0.1 have been grown and systematically characterized via X-Ray diffraction, magnetic, and transport measurements. The undoped sample is a heavily doped semiconductor with no sign of magnetic order down to 2 K. With increasing Pt content, the metallic behavior appears and superconductivity is realized for $x\geq$0.023. $T_{\rm c}$ rises to its maximum of approximately 13.6 K at the doping level of $x\sim$0.06, and then decreases for higher $x$ values. The electronic phase diagram of the 10-3-8 phase was mapped out based on the transport measurements. The mass anisotropy parameter $Γ\sim$10 obtained from resistive measurements in magnetic fields indicates a relatively large anisotropy in the iron-based superconductor family. This strong 2D character may lead to the absence of magnetic order. A linear $T$-dependence of susceptibility at high temperature is observed, indicating that spin fluctuations exist in the underdoped region as in most of the Fe-pnictide superconductors.
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Submitted 7 March, 2012;
originally announced March 2012.
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Transport and magnetic properties of La-doped CaFe$_2$As$_2$
Authors:
J. J. Ying,
J. C. Liang,
X. G. Luo,
X. F. Wang,
Y. J. Yan,
M. Zhang,
A. F. Wang,
Z. J. Xiang,
G. J. Ye,
P. Cheng,
X. H. Chen
Abstract:
We measured the transport properties and susceptibility of single crystals Ca$_{1-x}$La$_x$Fe$_2$As$_2$(x=0, 0.05, 0.1, 0.15, 0.19 and 0.25). Large in-plane resistivity anisotropy similar to that in Co-doped 122 iron-pnictides is observed although no transition metals were introduced in the FeAs-plane. The in-plane resistivity anisotropy gradually increases with La doping below T$_{SDW}$, being di…
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We measured the transport properties and susceptibility of single crystals Ca$_{1-x}$La$_x$Fe$_2$As$_2$(x=0, 0.05, 0.1, 0.15, 0.19 and 0.25). Large in-plane resistivity anisotropy similar to that in Co-doped 122 iron-pnictides is observed although no transition metals were introduced in the FeAs-plane. The in-plane resistivity anisotropy gradually increases with La doping below T$_{SDW}$, being different from the hole-doped 122 superconductors. The susceptibilities of the samples show that La doping leads to suppression of SDW and induces a Curie-Weiss-like behavior at low temperature, which is much stronger than the other 122 iron-based superconductors.
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Submitted 16 February, 2012;
originally announced February 2012.
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Phase diagram as a function of doping level and pressure in Eu$_{1-x}$La$_x$Fe$_2$As$_2$ system
Authors:
M. Zhang,
J. J. Ying,
Y. J. Yan,
A. F. Wang,
X. F. Wang,
Z. J. Xiang,
G. J. Ye,
P. Cheng,
X. G. Luo,
Jiangping Hu,
X. H. Chen
Abstract:
We establish the phase diagram of Eu$_{1-x}$La$_x$Fe$_2$As$_2$ system as a function of doping level x and the pressure by measuring the resistivity and magnetic susceptibility. The pressure can suppress the spin density wave (SDW) and structural transition very efficiently, while enhance the antiferromagnetic (AFM) transition temperature T$_N$ of Eu$^{2+}$. The superconductivity coexists with SDW…
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We establish the phase diagram of Eu$_{1-x}$La$_x$Fe$_2$As$_2$ system as a function of doping level x and the pressure by measuring the resistivity and magnetic susceptibility. The pressure can suppress the spin density wave (SDW) and structural transition very efficiently, while enhance the antiferromagnetic (AFM) transition temperature T$_N$ of Eu$^{2+}$. The superconductivity coexists with SDW order at the low pressure, while always coexists with the Eu$^{2+}$ AFM order. The results suggests that Eu$^{2+}$ spin dynamics is disentangeld with superconducting (SC) pairing taken place in the two-dimensional \emph{Fe-As} plane, but it can strongly affect superconducting coherence along c-axis.
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Submitted 9 January, 2012;
originally announced January 2012.
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SDW transition of Fe1 zigzag chains and metamagnetic transition of Fe2 in TaFe$_{1+y}$Te$_3$
Authors:
R. H. Liu,
M. Zhang,
P. Cheng,
Y. J. Yan,
Z. J. Xiang,
J. J. Ying,
X. F. Wang,
A. F. Wang,
G. J. Ye,
X. G. Luo,
X. H. Chen
Abstract:
We systematically study the AFM order of Fe1 zigzag chains and spin-flop of excess Fe2 under high magnetic field H through the susceptibility, magnetoresistance (MR), Hall effect and specific heat measurements in high-quality single crystal TaFe$_{1+y}$Te$_3$. These properties suggest that the high temperature AFM transition of the TaFeTe$_3$ layers should be a SDW-type AFM order. Below T$_N$, Fe1…
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We systematically study the AFM order of Fe1 zigzag chains and spin-flop of excess Fe2 under high magnetic field H through the susceptibility, magnetoresistance (MR), Hall effect and specific heat measurements in high-quality single crystal TaFe$_{1+y}$Te$_3$. These properties suggest that the high temperature AFM transition of the TaFeTe$_3$ layers should be a SDW-type AFM order. Below T$_N$, Fe1 antiferromangetic zigzag chains will induce a inner magnetic field \textbf{H$_{int}$} to interstitial Fe2 and lead Fe2 also forms an AFM alignment, in which the magnetic coupling strength between Fe1 and Fe2 is enhanced by decreasing temperature. On the other hand, the external magnetic field \textbf{H$_{ext}$} inclines to tune interstitial Fe2 to form FM alignment along \textbf{H$_{ext}$}. When \textbf{H$_{ext}$} arrives at the "coercive" field H$_C$, which is able to break the coupling between Fe1 and Fe2, these interstitial Fe2 atoms take a spin-flop from AFM to FM alignment. The local moment of Fe2 is about 4 $μ_{\textrm{B}}$/Fe. From low field ($<$H$_C$) AFM to high field ($>$H$_C$) FM for Fe2, it also induces sharp drop on resistivity and an anomalous Hall effect. The possible magnetic structure of TaFe$_{1+y}$Te$_3$ is proposed from the susceptibility and MR. The properties related to the spin-flop of Fe2 supply a good opportunity to study the coupling between Fe1 and Fe2 in these TaFe$_{1+y}$Te$_3$ or Fe$_{1+y}$Te with interstitial Fe2 compounds.
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Submitted 13 July, 2011;
originally announced July 2011.
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Magnetic properties in the doped spin-1/2 honeycomb-lattice compound In$_3$Cu$_2$VO$_9$
Authors:
Y. J. Yan,
Z. Y. Li,
T. Zhang,
X. G. Luo,
G. J. Ye,
Z. J. Xiang,
P. Cheng,
Liang-Jian Zou,
X. H. Chen
Abstract:
We report the magnetic properties in the Co- and Zn-doped spin-1/2 honeycomb-lattice compound In$_3$Cu$_2$VO$_9$. The magnetic susceptibility and specific heat experiments show no long-range ordering down to 2 K in In$_3$Cu$_2$VO$_9$. In the low temperature range, approximately T$^{2}$-dependent magnetic specific heat and linearly T-dependent spin susceptibility were observed, suggesting a spin li…
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We report the magnetic properties in the Co- and Zn-doped spin-1/2 honeycomb-lattice compound In$_3$Cu$_2$VO$_9$. The magnetic susceptibility and specific heat experiments show no long-range ordering down to 2 K in In$_3$Cu$_2$VO$_9$. In the low temperature range, approximately T$^{2}$-dependent magnetic specific heat and linearly T-dependent spin susceptibility were observed, suggesting a spin liquid candidate with a S = 1/2 honeycomb lattice. When Cu$^{2+}$ ions are partially substituted by Co$^{2+}$ ions, both impurity potential scattering and magnetic impurity scattering induced by magnetic Co$^{2+}$ ions break the homogenous spin-singlet spin liquid state, and lead to an antiferromagnetic(AFM) long-range correlation. While replacing Cu$^{2+}$ with nonmagnetic Zn$^{2+}$ ions, the frustration and antiferromagnetic correlation between Cu$^{2+}$ ions is weakened, leading to breakage of a spin liquid state and suppression of the low-dimensional AFM.
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Submitted 9 June, 2011;
originally announced June 2011.
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Coexistence of superconductivity and antiferromagnetism in single crystals $A_{0.8}Fe_{2-y}Se_2$ (A= K, Rb, Cs, Tl/K and Tl/Rb): evidence from magnetization and resistivity
Authors:
R. H. Liu,
X. G. Luo,
M. Zhang,
A. F. Wang,
J. J. Ying,
X. F. Wang,
Y. J. Yan,
Z. J. Xiang,
P. Cheng,
G. J. Ye,
Z. Y. Li,
X. H. Chen
Abstract:
We measure the resistivity and magnetic susceptibility in the temperature range from 5 K to 600 K for the single crystals $A$Fe$_{2-y}$Se$_2$ ($A$ = K$_{0.8}$, Rb$_{0.8}$, Cs$_{0.8}$, Tl$_{0.5}$K$_{0.3}$ and Tl$_{0.4}$Rb$_{0.4}$). A sharp superconducting transition is observed in low temperature resistivity and susceptibility, and susceptibility shows 100% Meissner volume fraction for all crystals…
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We measure the resistivity and magnetic susceptibility in the temperature range from 5 K to 600 K for the single crystals $A$Fe$_{2-y}$Se$_2$ ($A$ = K$_{0.8}$, Rb$_{0.8}$, Cs$_{0.8}$, Tl$_{0.5}$K$_{0.3}$ and Tl$_{0.4}$Rb$_{0.4}$). A sharp superconducting transition is observed in low temperature resistivity and susceptibility, and susceptibility shows 100% Meissner volume fraction for all crystals, while an antiferromagnetic transition is observed in susceptibility at Neel temperature ($T_N$) as high as 500 K to 540 K depending on A. It indicates the coexistence of superconductivity and antiferromagnetism. A sharp increase in resistivity arises from the structural transition due to Fe vacancy ordering at the temperature slightly higher than $T_{\rm N}$. Occurrence of superconductivity in an antiferromagnetic ordered state with so high $T_{\rm N}$ may suggest new physics in this type of unconventional superconductors.
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Submitted 14 February, 2011;
originally announced February 2011.
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Crystal structure, physical properties and superconductivity in $A_{x}$Fe$_2$Se$_2$ single crystals
Authors:
X. G. Luo,
X. F. Wang,
J. J. Ying,
Y. J. Yan,
Z. Y. Li,
M. Zhang,
A. F. Wang,
P. Cheng,
Z. J. Xiang,
G. J. Ye,
R. H. Liu,
X. H. Chen
Abstract:
We studied the correlation among structure and transport properties and superconductivity in the different $A_x$Fe$_2$Se$_2$ single crystals ($A$ = K, Rb, and Cs). Two sets of (00$l$) reflections are observed in the X-ray single crystal diffraction patterns, and arise from the intrinsic inhomogeneous distribution of the intercalated alkali atoms. The occurrence of superconductivity is closely rela…
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We studied the correlation among structure and transport properties and superconductivity in the different $A_x$Fe$_2$Se$_2$ single crystals ($A$ = K, Rb, and Cs). Two sets of (00$l$) reflections are observed in the X-ray single crystal diffraction patterns, and arise from the intrinsic inhomogeneous distribution of the intercalated alkali atoms. The occurrence of superconductivity is closely related to the {\sl c}-axis lattice constant, and the $A$ content is crucial to superconductivity. The hump observed in resistivity seems to be irrelevant to superconductivity. There exist many deficiencies within the FeSe layers in $A_x$Fe$_2$Se$_2$, while their $T_{\rm c}$ does not change so much. In this sense, superconductivity is robust to the Fe and Se vacancies. Very high resistivity in the normal state should arise from such defects in the conducting FeSe layers. $A_x$Fe$_2$Se$_2$ ($A$ = K, Rb, and Cs) single crystals show the same susceptibility behavior in the normal state, and no anomaly is observed in susceptibility at the hump temperature in resistivity. The clear jump in specific heat for Rb$_x$Fe$_2$Se$_2$ and K$_x$Fe$_2$Se$_2$ single crystals shows the good bulk superconductivity in these crystals.
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Submitted 29 January, 2011;
originally announced January 2011.
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Pressure effect on superconductivity of $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs)
Authors:
J. J. Ying,
X. F. Wang,
X. G. Luo,
Z. Y. Li,
Y. J. Yan,
M. Zhang,
A. F. Wang,
P. Cheng,
G. J. Ye,
Z. J. Xiang,
R. H. Liu,
X. H. Chen
Abstract:
We performed the high hydrostatic pressure resistivity measurements (up to 1.7 GPa) on the newly discovered superconductors $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs) single crystals. Two batches of single crystals $K_xFe_2Se_2$ with different transition temperatures ($T_c$) were used to study the effect of pressure. The $T_c$ of the first one gradually decreases with increasing pressure from 32.6 K at…
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We performed the high hydrostatic pressure resistivity measurements (up to 1.7 GPa) on the newly discovered superconductors $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs) single crystals. Two batches of single crystals $K_xFe_2Se_2$ with different transition temperatures ($T_c$) were used to study the effect of pressure. The $T_c$ of the first one gradually decreases with increasing pressure from 32.6 K at ambient pressure. While a dome-like behavior was observed for the crystal with $T_c=31.1$ K, and $T_c$ reaches its maximum value of 32.7 K at the pressure of 0.48 GPa. It indicates that there exists a optimal doping with maximum $T_c$ of 32.7K in $K_xFe_2Se_2$ system. The behavior of $T_c$ vs. pressure for $Cs_xFe_2Se_2$ also shows a dome-like behavior, and $T_c$ reaches its maximum value of 31.1 K at the pressure of 0.82 GPa. The hump observed in temperature dependence of resistivity for all the samples tends to shift to high temperature with increasing pressure. The resistivity hump could arise from the vacancy of Fe or Se.
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Submitted 6 January, 2011;
originally announced January 2011.
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Superconductivity and Magnetic Properties of high-quality single crystals of $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs)
Authors:
J. J. Ying,
X. F. Wang,
X. G. Luo,
A. F. Wang,
M. Zhang,
Y. J. Yan,
Z. J. Xiang,
R. H. Liu,
P. Cheng,
G. J. Ye,
X. H. Chen
Abstract:
We successfully grew the high-quality single crystals of $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs) by self-flux method. Sharp superconducting transition was observed for both types of crystals. The crystals show the onset superconducting transition temperatures ($T_{\rm c}$) of 31 K and 30 K for K- and Cs-compounds, respectively, with nearly 100% shielding fraction. The crystals show quite high resisti…
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We successfully grew the high-quality single crystals of $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs) by self-flux method. Sharp superconducting transition was observed for both types of crystals. The crystals show the onset superconducting transition temperatures ($T_{\rm c}$) of 31 K and 30 K for K- and Cs-compounds, respectively, with nearly 100% shielding fraction. The crystals show quite high resistivity in the normal state of more than 160 m$Ω$ cm and 1300 m$Ω$ cm maximum resistivity for $K_{0.86}Fe_2Se_{1.82}$ and $Cs_{0.86}Fe_{1.66}Se_{2}$ single crystals, respectively. Much larger upper critical field $H_{\rm c2}$ is inferred from low-temperature iso-magnetic-field magnetoresistance in these crystals than in FeSe. The anisotropy $H^{ab}_{\rm c2}$(0)/$H^{c}_{\rm c2}$(0) is around 3 for both of the two materials. Anisotropic peculiar magnetic behavior in normal state has been found for $Cs_{0.86}Fe_{1.66}Se_{2}$
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Submitted 26 December, 2010;
originally announced December 2010.
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Superconductivity at 32 K in single crystal Rb$_{0.78}$Fe$_2$Se$_{1.78}$}
Authors:
A. F. Wang,
J. J. Ying,
Y. J. Yan,
R. H. Liu,
X. G. Luo,
Z. Y. Li,
X. F. Wang,
M. Zhang,
G. J. Ye,
P. Cheng,
Z. J. Xiang,
X. H. Chen
Abstract:
We successfully grew the high-quality single crystal of Rb$_{0.78}$Fe$_2$Se$_{1.78}$, which shows sharp superconducting transition in magnetic susceptibility and electrical resistivity. Resistivity measurements show the onset superconducting transition ($T_{\rm c}$) at 32.1 K and zero resistivity at 30 K. From the low-temperature iso-magnetic-field magnetoresistance, large upper critical field…
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We successfully grew the high-quality single crystal of Rb$_{0.78}$Fe$_2$Se$_{1.78}$, which shows sharp superconducting transition in magnetic susceptibility and electrical resistivity. Resistivity measurements show the onset superconducting transition ($T_{\rm c}$) at 32.1 K and zero resistivity at 30 K. From the low-temperature iso-magnetic-field magnetoresistance, large upper critical field $H_{\rm c2}$(0) has been estimated as high as 180 T for in-plane field and 59 T for out-of-plane field. The anisotropy $H^{ab}_{\rm c2}$(0)/$H^{c}_{\rm c2}$(0) is around 3.0, right lying between those observed in K$_x$Fe$_2$Se$_2$ and Cs$_x$Fe$_2$Se$_2$.
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Submitted 26 December, 2010;
originally announced December 2010.
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Reentrant spin-glass behavior in $TlFe_{2-x}Se_2$ with the $ThCr_2Si_2$-type structure
Authors:
J. J. Ying,
A. F. Wang,
Z. J. Xiang,
X. G. Luo,
R. H. Liu,
X. F. Wang,
Y. J. Yan,
M. Zhang,
G. J. Ye,
P. Cheng,
X. H. Chen
Abstract:
We investigated the physical properties of $TlFe_{2-x}Se_2$ single crystals. The resistivity of $TlFe_{2-x}Se_2$ shows typical semiconductor behavior with an activation energy of 25 meV. DC susceptibility indicates an antiferromagnetic transition at about 450 K. Reentrant spin-glass (RSG) behavior was found at about 130 K through DC and AC magnetic measurements. The RSG behavior suggests the exist…
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We investigated the physical properties of $TlFe_{2-x}Se_2$ single crystals. The resistivity of $TlFe_{2-x}Se_2$ shows typical semiconductor behavior with an activation energy of 25 meV. DC susceptibility indicates an antiferromagnetic transition at about 450 K. Reentrant spin-glass (RSG) behavior was found at about 130 K through DC and AC magnetic measurements. The RSG behavior suggests the existence of a strong competition between ferromagnetic (FM) and antiferromagnetic (AFM) interactions due to Fe deficiencies. Strong electron-electron correlation may exist in this material and it is possibly a candidate of parent compound for high $T_c$ superconductors.
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Submitted 13 December, 2010;
originally announced December 2010.
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Distinct electronic nematicities between electron and hole underdoped iron pnictides
Authors:
J. J. Ying,
X. F. Wang,
T. Wu,
Z. J. Xiang,
R. H. Liu,
Y. J. Yan,
A. F. Wang,
M. Zhang,
G. J. Ye,
P. Cheng,
J. P. Hu,
X. H. Chen
Abstract:
We systematically investigated the in-plane resistivity anisotropy of electron-underdoped $EuFe_{2-x}Co_xAs_2$ and $BaFe_{2-x}Co_xAs_2$, and hole-underdoped $Ba_{1-x}K_xFe_2As_2$. Large in-plane resistivity anisotropy was found in the former samples, while {\it tiny} in-plane resistivity anisotropy was detected in the latter ones. When it is detected, the anisotropy starts above the structural tra…
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We systematically investigated the in-plane resistivity anisotropy of electron-underdoped $EuFe_{2-x}Co_xAs_2$ and $BaFe_{2-x}Co_xAs_2$, and hole-underdoped $Ba_{1-x}K_xFe_2As_2$. Large in-plane resistivity anisotropy was found in the former samples, while {\it tiny} in-plane resistivity anisotropy was detected in the latter ones. When it is detected, the anisotropy starts above the structural transition temperature and increases smoothly through it. As the temperature is lowered further, the anisotropy takes a dramatic enhancement through the magnetic transition temperature. We found that the anisotropy is universally tied to the presence of non-Fermi liquid T-linear behavior of resistivity. Our results demonstrate that the nematic state is caused by electronic degrees of freedom, and the microscopic orbital involvement in magnetically ordered state must be fundamentally different between the hole and electron doped materials.
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Submitted 13 December, 2010;
originally announced December 2010.