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Pressure-induced Superconductivity in AgSbTe2
Authors:
Sudaice Kazibwe,
Bishnu Karki,
Wencheng Lu,
Zhongxin Liang,
Minghong Sui,
Melissa Gooch,
Zhifeng Ren,
Pavan Hosur,
Timothy A. Strobel,
Ching-Wu Chu,
Liangzi Deng
Abstract:
AgSbTe2 is a well-known thermoelectric material with a high Seebeck coefficient and intrinsically low thermal conductivity, but its behavior under pressure remains largely unexplored. Here we report a systematic investigation of the structural, electronic, and transport properties of non-stoichiometric AgSbTe2 under high pressure. At ambient pressure, the material can be described as having a cubi…
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AgSbTe2 is a well-known thermoelectric material with a high Seebeck coefficient and intrinsically low thermal conductivity, but its behavior under pressure remains largely unexplored. Here we report a systematic investigation of the structural, electronic, and transport properties of non-stoichiometric AgSbTe2 under high pressure. At ambient pressure, the material can be described as having a cubic crystal structure that remains stable up to 21.7 GPa beyond which it loses long-range structural order, while its crystal system fully recovers upon decompression. Remarkably, superconductivity emerges at a very low pressure of 0.38 GPa with an onset superconducting critical temperature (Tc) of 3.2 K. Tc increases with increasing pressure, reaching 6.9 K at 31.9 GPa, and peaks at 7.4 K during decompression. Magnetic-field-dependent transport measurements and electronic structure calculations reveal an evolution of the superconducting state driven by an enhanced electronic density of states at the Fermi level under compression. Our findings uncover pressure-induced superconductivity in AgSbTe2 and demonstrate that pressure can effectively tune the electronic ground state of thermoelectric materials, extending their functionality beyond thermoelectric energy conversion.
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Submitted 18 March, 2026;
originally announced March 2026.
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Creation, stabilization, and study at ambient pressure of pressure-induced superconductivity in Bi$_{0.5}$Sb$_{1.5}$Te$_3$
Authors:
Liangzi Deng,
Busheng Wang,
Clayton Halbert,
Daniel J. Schulze,
Melissa Gooch,
Trevor Bontke,
Ting-Wei Kuo,
Xin Shi,
Shaowei Song,
Nilesh Salke,
Hung-Duen Yang,
Zhifeng Ren,
Russell J. Hemley,
Eva Zurek,
Rohit P. Prasankumar,
Ching-Wu Chu
Abstract:
In light of breakthroughs in superconductivity under high pressure, and considering that record critical temperatures (T$_c$s) across various systems have been achieved under high pressure, the primary challenge for higher Tc should no longer solely be to increase T$_c$ under extreme conditions but also to reduce, or ideally eliminate, the need for applied pressure in retaining pressure-induced or…
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In light of breakthroughs in superconductivity under high pressure, and considering that record critical temperatures (T$_c$s) across various systems have been achieved under high pressure, the primary challenge for higher Tc should no longer solely be to increase T$_c$ under extreme conditions but also to reduce, or ideally eliminate, the need for applied pressure in retaining pressure-induced or -enhanced superconductivity. The topological semiconductor Bi$_{0.5}$Sb$_{1.5}$Te$_3$ (BST) was chosen to demonstrate our approach to addressing this challenge and exploring its intriguing physics. Under pressures up to ~ 50 GPa, three superconducting phases (BST-I, -II, and -III) were observed. A superconducting phase in BST-I appears at ~ 4 GPa, without a structural transition, suggesting the possible topological nature of this phase. Using the pressure-quench protocol (PQP) recently developed by us, we successfully retained this pressure-induced phase at ambient pressure and revealed the bulk nature of the state. Significantly, this demonstrates recovery of a pressure-quenched sample from a diamond anvil cell at room temperature with the pressure-induced phase retained at ambient pressure. Other superconducting phases were retained in BST-II and -III at ambient pressure and subjected to thermal and temporal stability testing. Superconductivity was also found in BST with T$_c$ up to 10.2 K, the record for this compound series. While PQP maintains superconducting phases in BST at ambient pressure, both depressurization and PQP enhance its T$_c$, possibly due to microstructures formed during these processes, offering an added avenue to raise T$_c$. These findings are supported by our density-functional theory calculations.
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Submitted 3 February, 2025;
originally announced February 2025.
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Magnetic Kagome Superconductor CeRu$_2$
Authors:
L. Z. Deng,
M. Gooch,
H. X. Liu,
T. Bontke,
J. Y. You,
S. Shao,
J. X. Yin,
D. Schulze,
Y. G. Shi,
Y. P. Feng,
G. Chang,
Q. M. Si,
C. W. Chu
Abstract:
Materials with a kagome lattice provide a platform for searching for new electronic phases and investigating the interplay between correlation and topology. Various probes have recently shown that the kagome lattice can host diverse quantum phases with intertwined orders, including charge density wave states, bond density wave states, chiral charge order, and, rarely, superconductivity. However, r…
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Materials with a kagome lattice provide a platform for searching for new electronic phases and investigating the interplay between correlation and topology. Various probes have recently shown that the kagome lattice can host diverse quantum phases with intertwined orders, including charge density wave states, bond density wave states, chiral charge order, and, rarely, superconductivity. However, reports of the coexistence of superconductivity and magnetic order in kagome materials remain elusive. Here we revisit a magnetic superconductor CeRu$_2$ with a kagome network formed by Ru atoms. Our first-principles calculations revealed a kagome flat band near the Fermi surface, indicative of flat-band magnetism. At ambient pressure, CeRu$_2$ exhibits a superconducting transition temperature ($T_{\text{c}}$) up to ~ 6 K and a magnetic order at ~ 40 K. Notably, superconductivity and related behavior can be tuned by adjusting the amount of Ru. We conducted a systematic investigation of the superconductivity and magnetic order in CeRu$_2$ via magnetic, resistivity, and structural measurements under pressure up to ~ 168 GPa. An unusual phase diagram that suggests an intriguing interplay between the compound's superconducting order parameters has been constructed. A $T_{\text{c}}$ resurgence was observed above pressure of ~ 28 GPa, accompanied by the sudden appearance of a secondary superconducting transition. Our experiments have identified tantalizing phase transitions driven by high pressure and suggest that the superconductivity and magnetism in CeRu$_2$ are strongly intertwined.
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Submitted 5 April, 2022; v1 submitted 1 April, 2022;
originally announced April 2022.
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Pressure-induced high-temperature superconductivity retained at ambient
Authors:
Liangzi Deng,
Trevor Bontke,
Rabin Dahal,
Yu Xie,
Bin Gao,
Xue Li,
Ketao Yin,
Melissa Gooch,
Donald Rolston,
Tong Chen,
Zheng Wu,
Yanming Ma,
Pengcheng Dai,
Ching-Wu Chu
Abstract:
To raise the superconducting-transition temperature (Tc) has been the driving force for the long, sustained effort in superconductivity research. Recent progress in hydrides with Tcs up to 287 K under 267 GPa has heralded a new era of room-temperature superconductivity (RTS) with immense technological promise. Indeed, RTS has lifted the temperature barrier for the ubiquitous application of superco…
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To raise the superconducting-transition temperature (Tc) has been the driving force for the long, sustained effort in superconductivity research. Recent progress in hydrides with Tcs up to 287 K under 267 GPa has heralded a new era of room-temperature superconductivity (RTS) with immense technological promise. Indeed, RTS has lifted the temperature barrier for the ubiquitous application of superconductivity. Unfortunately, formidable pressure is required to attain such high Tcs. The most effective relief to this impasse is to remove the pressure needed while retaining the pressure-induced Tc without pressure. Here we show such a possibility in the pure and doped high-temperature superconductor (HTS) FeSe by retaining, at ambient via pressure-quenching (PQ), its Tc up to 37 K (quadrupling that of a pristine FeSe) and other pressure-induced phases. We have also observed that some phases remain stable without pressure at up to 300 K and for at least 7 days. The observations are in qualitative agreement with our ab initio simulations using the solid-state nudged elastic band (SSNEB) method. We strongly believe that the PQ technique developed here can be adapted to the RTS hydrides and other materials of value with minimal effort.
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Submitted 12 April, 2021;
originally announced April 2021.
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Pressure effects on magnetic ground states in cobalt doped multiferroic Mn$_{1-x}$Co$_{x}$WO$_4$
Authors:
Jinchen Wang,
Feng Ye,
Songxue Chi,
Jaime A. Fernandez-Baca,
Huibo Cao,
Wei Tian,
M. Gooch,
N. Poudel,
Yaqi Wang,
Bernd Lorenz,
C. W. Chu
Abstract:
Using ambient pressure x-ray and high pressure neutron diffraction, we studied the pressure effect on structural and magnetic properties of multiferroic Mn$_{1-x}$Co$_x$WO$_4$ single crystals ($x=0, 0.05, 0.135$ and $0.17$), and compared it with the effects of doping. Both Co doping and pressure stretch the Mn-Mn chain along the $c$~direction. At high doping level ($x=0.135$ and $0.17$), pressure…
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Using ambient pressure x-ray and high pressure neutron diffraction, we studied the pressure effect on structural and magnetic properties of multiferroic Mn$_{1-x}$Co$_x$WO$_4$ single crystals ($x=0, 0.05, 0.135$ and $0.17$), and compared it with the effects of doping. Both Co doping and pressure stretch the Mn-Mn chain along the $c$~direction. At high doping level ($x=0.135$ and $0.17$), pressure and Co doping drive the system in a similar way and induce a spin-flop transition for the $x=0.135$ compound. In contrast, magnetic ground states at lower doping level ($x=0$ and $0.05$) are robust against pressure but experience a pronounced change upon Co substitution. As Co introduces both chemical pressure and magnetic anisotropy into the frustrated magnetic system, our results suggest the magnetic anisotropy is the main driving force for the Co induced phase transitions at low doping level, and chemical pressure plays a more significant role at higher Co concentrations.
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Submitted 15 April, 2016;
originally announced April 2016.
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High pressure study of the normal and superconducting states of the layered pnictide oxide Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O with x = 0, 0.10, and 0.15
Authors:
M. Gooch,
P. Doan,
B. Lorenz,
Z. J. Tang,
A. M. Guloy,
C. W. Chu
Abstract:
Here we present a systematic study of the effects of pressure on the superconducting and spin/charge density wave (SDW/CDW) transitions of Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O (x = 0, 0.10, and 0.15) by means of resistivity measurements. For x = 0 and 0.10, external pressure results in a decease of the SDW/CDW transition temperature T$_c$; however, no measurable change is observed for the x = 0.15. The p…
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Here we present a systematic study of the effects of pressure on the superconducting and spin/charge density wave (SDW/CDW) transitions of Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O (x = 0, 0.10, and 0.15) by means of resistivity measurements. For x = 0 and 0.10, external pressure results in a decease of the SDW/CDW transition temperature T$_c$; however, no measurable change is observed for the x = 0.15. The pressure effect on the superconducting transition temperature is different for all three samples. For BaTi$_2$Sb$_2$O (x=0), T$_c$ increases significantly from 1.2 K at zero pressure to $\sim$ 2.9 K at 16.1 kbars. The 10 % Na-doped sample shows an initial T$_c$ increase up to 4.2 K with pressure which saturates at higher pressure values. For higher Na concentrations (x=0.15), T$_c$ continuously decreases with increasing pressure.
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Submitted 27 August, 2013;
originally announced August 2013.
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Weak Coupling BCS-like Superconductivity in the Pnictide Oxide Ba$_{1-x}$Na$_x$Ti$_2$Sb$_2$O (x=0 and 0.15)
Authors:
Melissa Gooch,
Phuong Doan,
Zhongjia Tang,
Bernd Lorenz,
Arnold M. Guloy,
Paul. C. W. Chu
Abstract:
We report the results of low-temperature heat capacity measurements of the pnictide oxide superconductor BaTi$_2$Sb$_2$O doped with sodium. The temperature and field dependent heat capacity data are well described by a single-gap BCS theory. The estimated values for the normal state Sommerfeld constant, the heat capacity jump at $T_c$, and the electron-phonon coupling constant are in favor of a co…
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We report the results of low-temperature heat capacity measurements of the pnictide oxide superconductor BaTi$_2$Sb$_2$O doped with sodium. The temperature and field dependent heat capacity data are well described by a single-gap BCS theory. The estimated values for the normal state Sommerfeld constant, the heat capacity jump at $T_c$, and the electron-phonon coupling constant are in favor of a conventional weak coupling superconductivity mediated by electron-phonon interaction. The results are discussed with regard to and compared with recent first principle calculations.
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Submitted 8 August, 2013;
originally announced August 2013.
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Ba1-xNaxTi2Sb2O (0.0 <= x <= 0.33): A Layered Titanium-based Pnictide Oxide Superconductor
Authors:
Phuong Doan,
Melissa Gooch,
Zhongjia Tang,
Bernd Lorenz,
Angela Möller,
Joshua Tapp,
Paul C. W. Chu,
Arnold M. Guloy
Abstract:
A new layered Ti-based pnictide oxide superconductor, Ba1-xNaxTi2Sb2O (0.0 <= x <= 0.33), is reported. X-ray studies reveal it crystallizes in the tetragonal CeCr2Si2C structure. The undoped parent compound, BaTi2Sb2O (P4/mmm; a=4.1196(1)Å; c=8.0951(2)Å), exhibits a CDW/SDW transition at 54K. Upon chemical doping with Na, the CDW/SDW transition is systematically suppressed and super-conductivity a…
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A new layered Ti-based pnictide oxide superconductor, Ba1-xNaxTi2Sb2O (0.0 <= x <= 0.33), is reported. X-ray studies reveal it crystallizes in the tetragonal CeCr2Si2C structure. The undoped parent compound, BaTi2Sb2O (P4/mmm; a=4.1196(1)Å; c=8.0951(2)Å), exhibits a CDW/SDW transition at 54K. Upon chemical doping with Na, the CDW/SDW transition is systematically suppressed and super-conductivity arises with the critical temperatures, Tc, increasing to 5.5 K. Bulk superconductivity is confirmed by resistivity, magnetic and heat capacity measurements. Like the high-Tc cuprates and the iron pnictides, superconductivity in BaTi2Sb2O arises from an ordered state. Similarities and differences to the cuprate and iron pnictide supercon-ductors are discussed.
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Submitted 17 April, 2013; v1 submitted 24 September, 2012;
originally announced September 2012.
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High-pressure study of superconducting and non-superconducting single crystals of the same nominal composition Rb0.8Fe2Se2
Authors:
M. Gooch,
B. Lv,
L. Z. Deng,
T. Muramatsu,
J. Meen,
Y. Y. Xue,
B. Lorenz,
C. W. Chu
Abstract:
Two single crystalline samples with the same nominal composition of Rb0.8Fe2Se2 prepared via slightly different precursor routes under the same thermal processing conditions were investigated at ambient and high pressures. One sample was found superconducting with a Tc of ~31 K without the previously reported resistivity-hump and the other was unexpectedly found to be a narrow-gap semiconductor. W…
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Two single crystalline samples with the same nominal composition of Rb0.8Fe2Se2 prepared via slightly different precursor routes under the same thermal processing conditions were investigated at ambient and high pressures. One sample was found superconducting with a Tc of ~31 K without the previously reported resistivity-hump and the other was unexpectedly found to be a narrow-gap semiconductor. While the high pressure data can be understood in terms of pressure-induced variation in doping, the detailed doping effect on superconductivity is yet to be determined.
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Submitted 27 October, 2011;
originally announced October 2011.
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Pressure effects on strained FeSe0.5Te0.5 thin films
Authors:
M. Gooch,
B. Lorenz,
S. X. Huang,
C. L. Chien,
C. W. Chu
Abstract:
The pressure effect on the resistivity and superconducting Tc of prestrained thin films of the iron chalcogenide superconductor FeSe0.5Te0.5 is studied. Films with different anion heights above the Fe layer showing different values of ambient pressure Tc's are compressed up to a pressure of 1.7 GPa. All films exhibit a significant increase of Tc with pressure. The results cannot solely be explaine…
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The pressure effect on the resistivity and superconducting Tc of prestrained thin films of the iron chalcogenide superconductor FeSe0.5Te0.5 is studied. Films with different anion heights above the Fe layer showing different values of ambient pressure Tc's are compressed up to a pressure of 1.7 GPa. All films exhibit a significant increase of Tc with pressure. The results cannot solely be explained by a pressure-induced decrease of the anion height but other parameters have to be considered to explain the data for all films.
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Submitted 22 August, 2011;
originally announced August 2011.
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The Unusual Superconducting State at 49 K in Electron-Doped CaFe2As2 at Ambient
Authors:
B. Lv,
L. Z. Deng,
M. Gooch,
F. Y. Wei,
Y. Y. Sun,
J. Meen,
Y. Y. Xue,
B. Lorenz,
C. W. Chu
Abstract:
We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe2As2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at ~ 49 K, which has a low critical field ~ 4 Oe, and the other at ~ 21 K, with a much higher critical field > 5 T. Our observations are in s…
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We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe2As2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at ~ 49 K, which has a low critical field ~ 4 Oe, and the other at ~ 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe2As2 (or Ae122), where Ae = Ca, Sr or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (Tc) only up to 38 K and pressurization has been reported to produce superconductivity with a Tc up to 30 K. The unusual 49 K phase detected will be discussed.
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Submitted 29 June, 2011; v1 submitted 10 June, 2011;
originally announced June 2011.
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The superconductor KxSr(1-x)Fe2As2: Normal state and superconducting properties
Authors:
B. Lv,
M. Gooch,
B. Lorenz,
F. Chen,
A. M. Guloy,
C. W. Chu
Abstract:
The normal state and superconducting properties are investigated in the phase diagram of K_xSr_{1-x}Fe_2As_2 for 0<x<1. The ground state upper critical field, H_{c2}(0), is extrapolated from magnetic field dependent resistivity measurements. H_{c2}(0) scales with the critical temperature, T_c, of the superconducting transition. In the normal state the Seebeck coefficient is shown to experience a…
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The normal state and superconducting properties are investigated in the phase diagram of K_xSr_{1-x}Fe_2As_2 for 0<x<1. The ground state upper critical field, H_{c2}(0), is extrapolated from magnetic field dependent resistivity measurements. H_{c2}(0) scales with the critical temperature, T_c, of the superconducting transition. In the normal state the Seebeck coefficient is shown to experience a dramatic change near a critical substitution of x=0.3. This is associated with the formation of a spin density wave state above the superconducting transition temperature. The results provide strong evidence for the reconstruction of the Fermi surface with the onset of magnetic order.
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Submitted 27 February, 2009;
originally announced March 2009.
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The Synthesis and Characterization of LiFeAs and NaFeAs
Authors:
C. W. Chu,
F. Chen,
M. Gooch,
A. M. Guloy,
B. Lorenz,
B. Lv,
K. Sasmal,
Z. J. Tang,
J. H. Tapp,
Y. Y. Xue
Abstract:
The newest homologous series of superconducting As-pnictides, LiFeAs (Li111) and NaFeAs (Na111) have been synthesized and investigated. Both crystallize with the layered tetragonal anti-PbFCl-type structure in P4/nmm space group. Polycrystalline samples and single-crystals of Li111 and Na111 display superconducting transitions at ~ 18 K and 12-25 K, respectively. No magnetic order has been found…
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The newest homologous series of superconducting As-pnictides, LiFeAs (Li111) and NaFeAs (Na111) have been synthesized and investigated. Both crystallize with the layered tetragonal anti-PbFCl-type structure in P4/nmm space group. Polycrystalline samples and single-crystals of Li111 and Na111 display superconducting transitions at ~ 18 K and 12-25 K, respectively. No magnetic order has been found in either compound, although a weak magnetic background is clearly in evidence. The origin of the carriers and the stoichiometric compositions of Li111 and Na111 were explored.
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Submitted 4 February, 2009;
originally announced February 2009.
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Pressure shift of the superconducting T_c of LiFeAs
Authors:
M. Gooch,
B. Lv,
J. H. Tapp,
Z. Tang,
B. Lorenz,
A. M. Guloy,
P. C. W. Chu
Abstract:
The effect of hydrostatic pressure on the superconductivity in LiFeAs is investigated up to 1.8 GPa. The superconducting transition temperature, T_c, decreases linearly with pressure at a rate of 1.5 K/GPa. The negative pressure coefficient of T_c and the high ambient pressure T_c indicate that LiFeAs is the high-pressure analogue of the isoelectronic SrFe_2As_2 and BaFe_2As_2.
The effect of hydrostatic pressure on the superconductivity in LiFeAs is investigated up to 1.8 GPa. The superconducting transition temperature, T_c, decreases linearly with pressure at a rate of 1.5 K/GPa. The negative pressure coefficient of T_c and the high ambient pressure T_c indicate that LiFeAs is the high-pressure analogue of the isoelectronic SrFe_2As_2 and BaFe_2As_2.
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Submitted 28 January, 2009;
originally announced January 2009.
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Evidence of quantum criticality in the phase diagram of K$_x$Sr$_{1-x}$Fe$_2$As$_2$ from measurements of transport and thermoelectricity
Authors:
Melissa Gooch,
Bing Lv,
Bernd Lorenz,
Arnold M. Guloy,
Ching-Wu Chu
Abstract:
The electrical transport and thermoelectric properties of K_xSr_{1-x}Fe_2As_2 are investigated for 0<x<1. The resistivity rho(T) shows a crossover from Fermi liquid-like temperature dependence at small x to linear rho~T dependence at x_c=0.4. With further increasing x, rho(T) becomes non-linear again. The thermoelectric power S(T) exhibits a similar crossover with increasing x with a logarithmic…
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The electrical transport and thermoelectric properties of K_xSr_{1-x}Fe_2As_2 are investigated for 0<x<1. The resistivity rho(T) shows a crossover from Fermi liquid-like temperature dependence at small x to linear rho~T dependence at x_c=0.4. With further increasing x, rho(T) becomes non-linear again. The thermoelectric power S(T) exhibits a similar crossover with increasing x with a logarithmic T-dependence, S/T~ln(T), near the critical doping x_c. These results provide evidence for a quantum critical behavior due to the coupling of low-energy conduction electrons to two-dimensional spin fluctuations.
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Submitted 5 March, 2009; v1 submitted 10 December, 2008;
originally announced December 2008.
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Pressure-induced shift of T$_c$ in K$_x$Sr$_{1-x}$Fe$_2$As$_2$ (x=0.2, 0.4, 0.7): Analogy to the high-T$_c$ cuprate superconductors
Authors:
Melissa Gooch,
Bing Lv,
Bernd Lorenz,
Arnold M. Guloy,
Ching-Wu Chu
Abstract:
The systematic pressure shifts of T_c were investigated in the whole phase diagram of the FeAs-based superconducting compound K_xSr_{1-x}Fe_2As_2. Different regions, arising from corresponding responses of T$_c$ to pressure (dT_c/dp>0, =0, or <0), can be clearly distinguished. This reveals an interesting similarity of the FeAs superconductors and the high-T_c cuprates. This behavior is a manifes…
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The systematic pressure shifts of T_c were investigated in the whole phase diagram of the FeAs-based superconducting compound K_xSr_{1-x}Fe_2As_2. Different regions, arising from corresponding responses of T$_c$ to pressure (dT_c/dp>0, =0, or <0), can be clearly distinguished. This reveals an interesting similarity of the FeAs superconductors and the high-T_c cuprates. This behavior is a manifestation of the layered structure of the FeAs compounds and the pressure-induced charge transfer between the (Fe_2As_2) and (K/Sr) layers. The coexistence of superconductivity and spin-density wave behavior were also observed, and the pressure effects on the latter is explored.
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Submitted 26 November, 2008; v1 submitted 11 September, 2008;
originally announced September 2008.