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Evidence for Anion-Free-Electron Duality and Enhanced Superconducting Role of Interstitial Anionic Electrons in Electrides
Authors:
Zhao Liu,
Xiang Wang,
Yin Yang,
Pengcheng Ma,
Zhijun Tu,
Xinyu Wang,
Donghan Jia,
Wenju Zhou,
Huiyang Gou,
Hechang Lei,
Qiang Xu,
Zhonghao Liu,
Tian Cui
Abstract:
The discovery of superconducting electrides, characterized by interstitial anionic electrons (IAEs) residing in lattice cavities, has established a distinctive platform for investigating superconductors. Yet the superconducting origin and the fundamental role of IAEs in Cooper pairing formation remain poorly understood due to the challenges in directly observing IAEs. Here, combining angle-resolve…
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The discovery of superconducting electrides, characterized by interstitial anionic electrons (IAEs) residing in lattice cavities, has established a distinctive platform for investigating superconductors. Yet the superconducting origin and the fundamental role of IAEs in Cooper pairing formation remain poorly understood due to the challenges in directly observing IAEs. Here, combining angle-resolved photoemission spectroscopy (ARPES), transport measurements, and first-principles calculations, we certify that the IAEs in electride La3In (Tc = 9.4 K) exhibit a dual nature as both anions and free electrons. With the finite-depth potential well model, we trace that IAEs originate from electronic states near the Fermi level located above potential barriers, forming a Fermi sea susceptible to scattering by La-derived phonons, triggering superconductivity. ARPES combined with high-resolution XRD measurements on oxygen-treated samples directly reveals IAEs' spatial distribution and energy dispersion from interstitial sites with the consistent energy value predicted by our theory model. The concomitant diminution of free electrons upon oxygen treatment, leading to a marked reduction in superconductivity, further provides compelling experimental evidence that IAEs actively participate in electron-phonon coupling. Our findings resolve the long-standing ambiguity regarding the electronic nature of IAEs, elucidate their enhancing superconductivity in the phonon-mediated mechanism, and provide a foundation for exploring advanced electride-based superconductors.
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Submitted 26 November, 2025;
originally announced November 2025.
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Imaging magnetic flux trapping in lanthanum hydride using diamond quantum sensors
Authors:
Yang Chen,
Junyan Wen,
Ze-Xu He,
Jing-Wei Fan,
Xin-Yu Pan,
Cheng Ji,
Huiyang Gou,
Xiaohui Yu,
Liucheng Chen,
Gang-Qin Liu
Abstract:
Lanthanum hydride has attracted significant attention in recent years due to its signatures of superconductivity at around 250 K (1, 2). However, the megabar pressures required for synthesize and maintain its state present extraordinary challenges for experiments, particularly in characterizing its Meissner effect (3, 4). The nitrogen-vacancy (NV) center in diamond has emerged as a promising quant…
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Lanthanum hydride has attracted significant attention in recent years due to its signatures of superconductivity at around 250 K (1, 2). However, the megabar pressures required for synthesize and maintain its state present extraordinary challenges for experiments, particularly in characterizing its Meissner effect (3, 4). The nitrogen-vacancy (NV) center in diamond has emerged as a promising quantum probe to address this problem (5-8), but a gap remains between its working pressure and the pressure required to study the superconducting state of lanthanum hydride (9-12). In this work, using neon gas as the pressure transmitting medium, the working pressure of NV centers is extended to nearly 200 GPa. This quantum probe is then applied to study the Meissner effect of a LaH$_{9.6}$ sample, synthesized by laser heating ammonia borane and lanthanum. A strong magnetic shielding effect is observed, with the transition temperature beginning at around 180 K and completing at 220 K. In addition, magnetic field imaging after field cooling reveals strong flux trapping and significant inhomogeneities within the sample. Our work provides compelling evidence for superconductivity in lanthanum hydride and highlights the importance of spatially resolved techniques in characterizing samples under ultrahigh pressure conditions.
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Submitted 23 October, 2025;
originally announced October 2025.
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High Pressure Superconducting transition in Dihydride BiH$_2$ with Bismuth Open-Channel Framework
Authors:
Liang Ma,
Xin Yang,
Mei Li,
Pengfei Shan,
Ziyi Liu,
Jun Hou,
Sheng Jiang,
Lili Zhang,
Chuanlong Lin,
Pengtao Yang,
Bosen Wang,
Jianping Sun,
Yang Ding,
Huiyang Gou,
Haizhong Guo,
Jinguang Cheng
Abstract:
Metal hydrides MHx with low hydrogen content are not expected to show high-Tc superconductivity owing to the low hydrogen-derived electronic density of states at Fermi level and the limited hydrogen contribution to electron-phonon coupling strength. In this work, we report on the successful synthesis of a novel bismuth dihydride superconductor, Cmcm-BiH$_2$, at approximately 150 GPa, and the disco…
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Metal hydrides MHx with low hydrogen content are not expected to show high-Tc superconductivity owing to the low hydrogen-derived electronic density of states at Fermi level and the limited hydrogen contribution to electron-phonon coupling strength. In this work, we report on the successful synthesis of a novel bismuth dihydride superconductor, Cmcm-BiH$_2$, at approximately 150 GPa, and the discovery of superconductivity with Tc about 62 K at 163 GPa, marking the first instance of superconductor among the MH$_2$-type metal dihydrides. Cmcm-BiH$_2$ adopts a unique host-guest type structure, in which the Bi atoms via weak Bi-Bi covalent bonds form a three-dimensional open-channel framework that encapsulates H$_2$-like molecules as guests, thereby broadening the structural diversity of hydrides under high pressures. The occurrence of superconductivity is evidenced by a sharp drop of resistivity to zero and the characteristic downward shift of Tc under applied magnetic fields. Notably, Cmcm-BiH$_2$ remains stable down to at least 97 GPa during decompression, with the calculated lowest pressure for dynamic stability of 10 GPa. In-depth analysis reveals that the covalent bismuth open-channel structure forms metallic conduction channels, dominates the electronic states near the Fermi level, and contributes approximately 51% of the total $lambda$ in Cmcm-BiH$_2$, distinguishing it from known high-pressure hydride superconductors. These findings highlight the critical role of non-hydrogen elements in producing superconductivity and open new avenues for the design and optimization of high-Tc hydride superconductors.
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Submitted 24 October, 2025;
originally announced October 2025.
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Relationship among Structural, Disordered, Magnetism and Band Topology in MnSb2Te4(Sb2Te3)n Family
Authors:
Ming Xi,
Yuchong Zhang,
Wenju Zhou,
Famin Chen,
Donghan Jia,
Huiyang Gou,
Tian Qian,
Hechang Lei
Abstract:
Interplay between topology and magnetism induces various exotic quantum phenomena, with magnetic topological insulators (MTIs) serving as a prominent example due to their ability to host the quantum anomalous Hall effect (QAHE). However, the realization of QAHE at higher temperature approaching magnetic-transition-temperature remains a significant challenge, primarily due to the scarcity of suitab…
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Interplay between topology and magnetism induces various exotic quantum phenomena, with magnetic topological insulators (MTIs) serving as a prominent example due to their ability to host the quantum anomalous Hall effect (QAHE). However, the realization of QAHE at higher temperature approaching magnetic-transition-temperature remains a significant challenge, primarily due to the scarcity of suitable material platforms and limited understanding of the intricate relationships between band topology, magnetism, and defects. Here, we report a comprehensive investigation of MnSb2Te4(Sb2Te3)n (n = 0 - 5) single crystals, including the discovery of novel MnSb8Te13 pure phase. Experimental measurements confirm that MnSb8Te13 exhibits ferromagnetism and features topologically nontrivial electronic structures, characterized by a Dirac point located further from the conduction band and a possible larger bulk gap compared to MnBi2Te4(Bi2Te3)n (n = 0 - 3). Moreover, we systematically analyze the relationship between structure, magnetism, topology, and disorder within Mn(Sb, Bi)2Te4((Sb, Bi)2Te3)n family. Present work will shed light on the exploration of potential platforms capable of achieving QAHE near magnetic transition temperature, offering new directions for advancing topological quantum materials.
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Submitted 10 October, 2025;
originally announced October 2025.
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Superconductivity in cubic La3Al with interstitial anionic electrons
Authors:
Zhijun Tu,
Peihan Sun,
Donghan Jia,
Huiyang Gou,
Kai Liu,
Hechang Lei
Abstract:
We report the observation of superconductivity in cubic La3Al single crystal. It shows a metallic behavior at a normal state without observable structural transition and enters the superconducting state below Tc ~ 6.32 K. Detailed characterizations and analysis indicate that cubic La3Al is a bulk type-II BCS superconductor. Moreover, theoretical calculations show that it can host interstitial anio…
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We report the observation of superconductivity in cubic La3Al single crystal. It shows a metallic behavior at a normal state without observable structural transition and enters the superconducting state below Tc ~ 6.32 K. Detailed characterizations and analysis indicate that cubic La3Al is a bulk type-II BCS superconductor. Moreover, theoretical calculations show that it can host interstitial anionic electrons, which are located at the body center of cubic unit cell, and confirm the electron-phonon coupling as the superconducting mechamism. Thus, cubic La3Al can be regarded as an novel electride superconductor.
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Submitted 26 September, 2025;
originally announced September 2025.
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Three-Dimensional Continuous Multi-Walled Carbon Nanotubes Network-Toughened Diamond Composite
Authors:
Jiawei Zhang,
Keliang Qiu,
Tengfei Xu,
Xi Shen,
Junkai Li,
Fengjiao Li,
Richeng Yu,
Huiyang Gou,
Duanwei He,
Liping Wang,
Zhongzhou Wang,
Guodong Li,
Yusheng Zhao,
Ke Chen,
Fang Hong,
Ruifeng Zhang,
Xiaohui Yu
Abstract:
Enhancing the fracture toughness of diamond while preserving its hardness is a significant challenge. Traditional toughening strategies have primarily focused on modulating the internal microstructural units of diamonds, including adjustments to stacking sequences, faults, nanotwinning, and the incorporation of amorphous phases, collectively referred to as intrinsic toughening. Here, we introduce…
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Enhancing the fracture toughness of diamond while preserving its hardness is a significant challenge. Traditional toughening strategies have primarily focused on modulating the internal microstructural units of diamonds, including adjustments to stacking sequences, faults, nanotwinning, and the incorporation of amorphous phases, collectively referred to as intrinsic toughening. Here, we introduce an extrinsic toughening strategy to develop an unparalleled tough diamond composite with complex and abundant sp2-sp3 bonding interfaces, by incorporating highly dispersed multi-walled carbon nanotubes (MWCNTs) into the gaps of diamond grains to create a three-dimensional (3D) continuous MWCTNs network-toughen heterogeneous structure. The resultant composite exhibits a hardness of approximately 91.6 GPa and a fracture toughness of roughly 36.4 MPa.m1/2, which is six times higher than that of synthetic diamond and even surpasses that of tungsten alloys, surpassing the benefits achievable through intrinsic toughening alone. The remarkable toughening behavior can be attributed to the formation of numerous mixed sp2-sp3 bonding interactions at the 3D continuous network MWCNTs/diamond interfaces, which facilitate efficient energy dissipation. Our 3D continuous network heterogeneous structure design provides an effective approach for enhancing the fracture toughness of superhard materials, offering a new paradigm for the advanced composite ceramics.
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Submitted 25 August, 2025;
originally announced August 2025.
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New phase space of hardness materials and synergic enhancement of hardness and toughness in superconducting Ti2Co and Ti4Co2X (X = B, C, N, O)
Authors:
Lifen Shi,
Keyuan Ma,
Jingyu Hou,
Pan Ying,
Ningning Wang,
Xiaojun Xiang,
Pengtao Yang,
Xiaohui Yu,
Huiyang Gou,
Jianping Sun,
Yoshiya Uwatoko,
Fabian O. von Rohr,
Xiang-Feng Zhou,
Bosen Wang,
Jinguang Cheng
Abstract:
Compared to traditional superhard materials with high electron density and strong covalent bonds, alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness. Breaking through the limits of alloy materials is a preface and long term topic, which is of great significance and value for improving the comprehensive mechanical properties of alloy mat…
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Compared to traditional superhard materials with high electron density and strong covalent bonds, alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness. Breaking through the limits of alloy materials is a preface and long term topic, which is of great significance and value for improving the comprehensive mechanical properties of alloy materials. Here, we report on the discovery of a cubic alloy semiconducting material Ti2Co with large Vickers of hardness Hvexp = 6.7 GPa and low fracture toughness of KICexp =1.51 MPa m0.5. Unexpectedly, the former value is nearly triple of the Hvcal = 2.66 GPa predicted by density functional theory (DFT) calculations and the latter value is about one or two orders of magnitude smaller than that of ordinary titanium alloy materials (KICexp = 30-120 MPa m0.5).These specifications place Ti2Co far from the phase space of the known alloy materials, but close to medium hardness materials such as MgO or TiO2. Upon incorporation of oxygen into structural void positions, both values were simultaneously improved for Ti4Co2O to = 9.7 GPa and 2.19 MPa m0.5, respectively. Further DFT calculations on the electron localization function of Ti4Co2X (X = B, C, N, O) vs. the interstitial elements indicate that these simultaneous improvements originate from the coexistence of Ti-Co metallic bonds, the emergence of newly oriented Ti-X covalent bonds, and the increase of electron concentration. Moreover, the large difference between Hvexp and Hvcal of Ti2Co suggests underlying mechanism concerning the absence of the O(16d) or Ti2-O bonds in the O-(Ti2)6 octahedron.Our discovery expands the phase space of alloy materials and illuminates the path of exploring superconducting materials with excellent mechanical performances.
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Submitted 24 January, 2025;
originally announced January 2025.
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Superconductivity in pressurized trilayer La$_4$Ni$_3$O$_{10-δ}$ single crystals
Authors:
Yinghao Zhu,
Di Peng,
Enkang Zhang,
Bingying Pan,
Xu Chen,
Lixing Chen,
Huifen Ren,
Feiyang Liu,
Yiqing Hao,
Nana Li,
Zhenfang Xing,
Fujun Lan,
Jiyuan Han,
Junjie Wang,
Donghan Jia,
Hongliang Wo,
Yiqing Gu,
Yimeng Gu,
Li Ji,
Wenbin Wang,
Huiyang Gou,
Yao Shen,
Tianping Ying,
Xiaolong Chen,
Wenge Yang
, et al. (5 additional authors not shown)
Abstract:
The pursuit of discovering new high-temperature superconductors that diverge from the copper-based paradigm1-3 carries profound implications for elucidating mechanisms behind superconductivity and may also enable new applications4-8. Here, our investigation reveals that application of pressure effectively suppresses the spin and charge order in trilayer nickelate La4Ni3O10-δ single crystals, leadi…
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The pursuit of discovering new high-temperature superconductors that diverge from the copper-based paradigm1-3 carries profound implications for elucidating mechanisms behind superconductivity and may also enable new applications4-8. Here, our investigation reveals that application of pressure effectively suppresses the spin and charge order in trilayer nickelate La4Ni3O10-δ single crystals, leading to the emergence of superconductivity with a maximum critical temperature (Tc) of around 30 K at 69.0 GPa. The DC susceptibility measurements confirm a substantial diamagnetic response below Tc, indicating the presence of bulk superconductivity with a volume fraction exceeding 80%. In the normal state, we observe a "strange metal" behavior, characterized by a linear temperature-dependent resistance extending up to 300 K. Furthermore, the layer-dependent superconductivity observed hints at a unique interlayer coupling mechanism specific to nickelates, setting them apart from cuprates in this regard. Our findings provide crucial insights into the fundamental mechanisms underpinning superconductivity, while also introducing a new material platform to explore the intricate interplay between the spin/charge order, flat band structures, interlayer coupling, strange metal behavior and high-temperature superconductivity.
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Submitted 9 July, 2024; v1 submitted 13 November, 2023;
originally announced November 2023.
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Pressure-induced Superconductivity and Topological Quantum Phase Transitions in the Topological Semimetal ZrTe2
Authors:
Shihao Zhu,
Juefei Wu,
Peng Zhu,
Cuiying Pei,
Qi Wang,
Donghan Jia,
Xinyu Wang,
Yi Zhao,
Lingling Gao,
Changhua Li,
Weizheng Cao,
Mingxin Zhang,
Lili Zhang,
Mingtao Li,
Huiyang Gou,
Wenge Yang,
Jian Sun,
Yulin Chen,
Zhiwei Wang,
Yugui Yao,
Yanpeng Qi
Abstract:
Topological transition metal dichalcogenides (TMDCs) have attracted much attention due to its potential applications in spintronics and quantum computations. In this work, we systematically investigate the structural and electronic properties of topological TMDCs candidate ZrTe2 under high pressure. A pressure-induced Lifshitz transition is evidenced by the change of charge carrier type as well as…
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Topological transition metal dichalcogenides (TMDCs) have attracted much attention due to its potential applications in spintronics and quantum computations. In this work, we systematically investigate the structural and electronic properties of topological TMDCs candidate ZrTe2 under high pressure. A pressure-induced Lifshitz transition is evidenced by the change of charge carrier type as well as the Fermi surface. Superconductivity was observed at around 8.3 GPa without structural phase transition. A typical dome-shape phase diagram is obtained with the maximum Tc of 5.6 K for ZrTe2. Furthermore, our theoretical calculations suggest the presence of multiple pressure-induced topological quantum phase transitions, which coexists with emergence of superconductivity. The results demonstrate that ZrTe2 with nontrivial topology of electronic states display new ground states upon compression.
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Submitted 19 October, 2023;
originally announced October 2023.
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Unusual Nonlinear Optical Responses in Layered Ferroelectric Niobium Oxide Dihalides: Origin and Manipulation
Authors:
Liangting Ye,
Wenju Zhou,
Dajian Huang,
Xiao Jiang,
Donghan Jia,
Qiangbing Guo,
Dequan Jiang,
Yonggang Wang,
Xiaoqiang Wu,
Yang Li,
Huiyang Gou,
Bing Huang
Abstract:
Realization of large and highly tunable second-order nonlinear optical (NLO) responses, e.g., second-harmonic generation (SHG) and bulk photovoltaic effect (BPVE), is critical for developing modern optical and optoelectronic devices. Very recently, the two-dimensional van der Waals ferroelectric NbOX2 (X = Cl, Br or I) are discovered to exhibit unusually large and anisotropic SHG. However, the phy…
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Realization of large and highly tunable second-order nonlinear optical (NLO) responses, e.g., second-harmonic generation (SHG) and bulk photovoltaic effect (BPVE), is critical for developing modern optical and optoelectronic devices. Very recently, the two-dimensional van der Waals ferroelectric NbOX2 (X = Cl, Br or I) are discovered to exhibit unusually large and anisotropic SHG. However, the physical origin and possible tunability of NLO responses in NbOX2 remain to be unclear. In this article, we reveal that the large SHG in NbOCl2 is dominated by the synergy between large transition dipole moment and band-nesting-induced large intensity of electron-hole pairs. Remarkably, the NbOCl2 can exhibit dramatically different strain-dependent BPVE under different polarized light, originating from the interesting light-polarization-dependent orbital transition. Importantly, we successfully achieve a reversible ferroelectric-to-antiferroelectric phase transition via controlling ambient temperature or external pressure, accompanied by the greatly tunable NLO responses. Furthermore, we discover that the evolutions of SHG and BPVE in NbOX2 with variable X obey different rules. Our study provides a deep understanding on the novel NLO physics in NbOX2 and establishes great external-field tunability for device applications.
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Submitted 24 February, 2023;
originally announced February 2023.
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Pressure-Induced Superconductivity in Topological Heterostructure (PbSe)5(Bi2Se3)6
Authors:
Cuiying Pei,
Peng Zhu,
Bingtan Li,
Yi Zhao,
Lingling Gao,
Changhua Li,
Shihao Zhu,
Qinghua Zhang,
Tianping Ying,
Lin Gu,
Bo Gao,
Huiyang Gou,
Yansun Yao,
Jian Sun,
Hanyu Liu,
Yulin Chen,
Zhiwei Wang,
Yugui Yao,
Yanpeng Qi
Abstract:
Recently, the natural heterostructure of (PbSe)5(Bi2Se3)6 has been theoretically predicted and experimentally confirmed as a topological insulator. In this work, we induce superconductivity in (PbSe)5(Bi2Se3)6 by implementing high pressure. As increasing pressure up to 10 GPa, superconductivity with Tc ~ 4.6 K suddenly appears, followed by an abrupt decrease. Remarkably, upon further compression a…
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Recently, the natural heterostructure of (PbSe)5(Bi2Se3)6 has been theoretically predicted and experimentally confirmed as a topological insulator. In this work, we induce superconductivity in (PbSe)5(Bi2Se3)6 by implementing high pressure. As increasing pressure up to 10 GPa, superconductivity with Tc ~ 4.6 K suddenly appears, followed by an abrupt decrease. Remarkably, upon further compression above 30 GPa, a new superconducting state arises, where pressure raises the Tc to an unsaturated 6.0 K within the limit of our research. Combining XRD and Raman spectroscopies, we suggest that the emergence of two distinct superconducting states occurs concurrently with the pressure-induced structural transition in this topological heterostructure (PbSe)5(Bi2Se3)6.
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Submitted 3 January, 2023;
originally announced January 2023.
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Insulator-metal-superconductor transition in medium-entropy van der Waals compound MEPSe3 (ME=Fe, Mn, Cd, and In) under high pressures
Authors:
Xu Chen,
Junjie Wang,
Tianping Ying,
Dajian Huang,
Huiyang Gou,
Qinghua Zhang,
Yanchun Li,
Hideo Hosono,
Jian-gang Guo,
Xiaolong Chen
Abstract:
MPX3 (M=metals, X=S or Se) represents a large family of van der Waals (vdW) materials featuring with P-P dimers of ~2.3 Å separation. Its electrical transport property and structure can hardly be tuned by the intentional chemical doping and ionic intercalation. Here, we employ an entropy-enhancement strategy to successfully obtain a series of medium-entropy compounds MEPSe3 (ME=Fe, Mn, Cd and In),…
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MPX3 (M=metals, X=S or Se) represents a large family of van der Waals (vdW) materials featuring with P-P dimers of ~2.3 Å separation. Its electrical transport property and structure can hardly be tuned by the intentional chemical doping and ionic intercalation. Here, we employ an entropy-enhancement strategy to successfully obtain a series of medium-entropy compounds MEPSe3 (ME=Fe, Mn, Cd and In), in which the electrical and magnetic properties changed simultaneously. Lone-pair electrons of P emerge due to the dissociation of the dimers as evidenced by a 35% elongation in the P-P interatomic distance. The band gap widens from 0.1 eV to 0.7 eV by this dissociation. Under external physical pressure up to ~50 GPa, a giant collapse of up to 15% in the c-axis happens, which is in contrast to the in-plane shrinkage of their counterparts Fe/MnPSe3. It leads to the recombination of P3- with lone pair electrons into a P-P dimer and the smallest bulk modulus of 28 GPa in MPX3. The MEPSe3 transits from a spin-glass insulator to metal, and to superconductor, which is rarely observed in the MPX3. Our findings highlight the P-P dimer as an indicator to probe diverse electronic structure and the effectiveness of entropy-enhancement in materials science.
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Submitted 22 August, 2022; v1 submitted 18 July, 2022;
originally announced July 2022.
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Unconventional Excitonic States with Phonon Sidebands in Layered Silicon Diphosphide
Authors:
Ling Zhou,
Junwei Huang,
Lukas Windgaetter,
Chin Shen Ong,
Xiaoxu Zhao,
Caorong Zhang,
Ming Tang,
Zeya Li,
Caiyu Qiu,
Simone Latini,
Yangfan Lu,
Di Wu,
Huiyang Gou,
Andrew T. S. Wee,
Hideo Hosono,
Steven G. Louie,
Peizhe Tang,
Angel Rubio,
Hongtao Yuan
Abstract:
Many-body interactions between quasiparticles (electrons, excitons, and phonons) have led to the emergence of new complex correlated states and are at the core of condensed matter physics and material science. In low-dimensional materials, unique electronic properties for these correlated states could significantly affect their optical properties. Herein, combining photoluminescence, optical refle…
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Many-body interactions between quasiparticles (electrons, excitons, and phonons) have led to the emergence of new complex correlated states and are at the core of condensed matter physics and material science. In low-dimensional materials, unique electronic properties for these correlated states could significantly affect their optical properties. Herein, combining photoluminescence, optical reflection measurements and theoretical calculations, we demonstrate an unconventional excitonic state and its bound phonon sideband in layered silicon diphosphide (SiP$_2$), in which the bound electron-hole pair is composed of electrons confined within one-dimensional phosphorus$-$phosphorus chains and holes extended in two-dimensional SiP$_2$ layers. The excitonic state and the emergent phonon sideband show linear dichroism and large energy redshifts with increasing temperature. Within the $GW$ plus Bethe$-$Salpeter equation calculations and solving the generalized Holstein model non-perturbatively, we confirm that the observed sideband feature results from the correlated interaction between excitons and optical phonons. Such a layered material provides a new platform to study excitonic physics and many-particle effects.
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Submitted 16 June, 2022; v1 submitted 16 June, 2022;
originally announced June 2022.
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Ultrathin quantum light source enabled by a nonlinear van der Waals crystal with vanishing interlayer-electronic-coupling
Authors:
Qiangbing Guo,
Xiao-Zhuo Qi,
Meng Gao,
Sanlue Hu,
Lishu Zhang,
Wenju Zhou,
Wenjie Zang,
Xiaoxu Zhao,
Junyong Wang,
Bingmin Yan,
Mingquan Xu,
Yun-Kun Wu,
Goki Eda,
Zewen Xiao,
Huiyang Gou,
Yuan Ping Feng,
Guang-Can Guo,
Wu Zhou,
Xi-Feng Ren,
Cheng-Wei Qiu,
Stephen J. Pennycook,
Andrew T. S. Wee
Abstract:
Interlayer electronic coupling in two-dimensional (2D) materials enables tunable and emergent properties by stacking engineering. However, it also brings significant evolution of electronic structures and attenuation of excitonic effects in 2D semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical nonlinearities in transition metal dichalcogenides when monolayer…
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Interlayer electronic coupling in two-dimensional (2D) materials enables tunable and emergent properties by stacking engineering. However, it also brings significant evolution of electronic structures and attenuation of excitonic effects in 2D semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical nonlinearities in transition metal dichalcogenides when monolayers are stacked into van der Waals structures. Here we report a novel van der Waals crystal, niobium oxide dichloride, featuring a vanishing interlayer electronic coupling and scalable second harmonic generation intensity of up to three orders higher than that of exciton-resonant monolayer WS2. Importantly, the strong second-order nonlinearity enables correlated parametric photon pair generation, via a spontaneous parametric down-conversion (SPDC) process, in flakes as thin as ~46 nm. To our knowledge, this is the first SPDC source unambiguously demonstrated in 2D layered materials, and the thinnest SPDC source ever reported. Our work opens an avenue towards developing van der Waals material-based ultracompact on-chip SPDC sources, and high-performance photon modulators in both classical and quantum optical technologies.
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Submitted 8 February, 2022;
originally announced February 2022.
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Lonsdaleite: The diamond with optimized bond lengths and enhanced hardness
Authors:
Liuxiang Yang,
Kah Chun Lau,
Zhidan Zeng,
Dongzhou Zhang,
Hu Tang,
Bingmin Yan,
Huiyang Gou,
Yanping Yang,
Yuming Xiao,
Duan Luo,
Srilok Srinivasan,
Subramanian Sankaranarayanan,
Wenge Yang,
Jianguo Wen,
Ho-kwang Mao
Abstract:
Diamond is known as the hardest substance due to its ultra-strong tetrahedral sp3 carbon bonding framework. The only weak link is its cubic cleavage planes between (111) buckled honeycomb layers. Compressing graphite single crystals and heating to moderate temperatures, we synthesized a bulk, pure, hexagonal diamond (lonsdaleite) with distorted carbon tetrahedrons that shorten the bond between its…
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Diamond is known as the hardest substance due to its ultra-strong tetrahedral sp3 carbon bonding framework. The only weak link is its cubic cleavage planes between (111) buckled honeycomb layers. Compressing graphite single crystals and heating to moderate temperatures, we synthesized a bulk, pure, hexagonal diamond (lonsdaleite) with distorted carbon tetrahedrons that shorten the bond between its hexagonal (001) buckled honeycomb layers, thus strengthening their linkage. We observed direct transformation of graphite (100) to lonsdaleite (002) and graphite (002) to lonsdaleite (100). We find the bulk lonsdaleite has superior mechanical properties of Vicker hardnesses HV = 164+/-11 GPa and 124+/-13 GPa, measured on the surface corresponding to the original graphite (001) and (100) surfaces, respectively. Properties of lonsdaleite as the supreme material can be further enhanced by purifying the starting material graphite carbon and fine-tuning the high pressure-temperature synthesis conditions.
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Submitted 17 November, 2021;
originally announced November 2021.
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Evolution of Superatomic-Charge-density-wave and Superconductivity under Pressure in AuTe$_2$Se$_{4/3}$
Authors:
Xu Chen,
Ge Fei,
Yanpeng Song,
Tianping Ying,
Dajian Huang,
Bingying Pan,
Xiaofan Yang,
Keyu Chen,
Xinhui Zhan,
Junjie Wang,
Huiyang Gou,
Xin Chen,
Shiyan Li,
Jinguang Cheng,
Xiaobing Liu,
Hideo Hosono,
Jian-gang Guo,
Xiaolong Chen
Abstract:
Superatomic crystal is a class of hierarchical materials composed of atomically precise clusters assembled via van der Waals or covalent-like interactions. AuTe$_2$Se$_{4/3}$, an all-inorganic superatomic superconductor exhibiting superatomic-charge-density-wave (S-CDW), provides a first platform to study the response of their collectively quantum phenomenon to the external pressure in superatomic…
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Superatomic crystal is a class of hierarchical materials composed of atomically precise clusters assembled via van der Waals or covalent-like interactions. AuTe$_2$Se$_{4/3}$, an all-inorganic superatomic superconductor exhibiting superatomic-charge-density-wave (S-CDW), provides a first platform to study the response of their collectively quantum phenomenon to the external pressure in superatomic crystals. We reveal a competition between S-CDW and superconductivity using cutting-edge measurements on thin flakes at low pressures. Prominently, the pressure modulation of S-CDW ordering is 1$\sim$2 order of magnitudes (0.1 GPa) lower than that of conventional atomic superconductors. As pressure increases to 2.5 GPa, the $T_{\mathrm{CDW}}$ is suppressed and the superconducting transition temperature ($T_{\mathrm{c}}$) is firstly enhanced, and reaches the maximum then quenches with increasing pressure. Above 7.3 GPa, a second superconducting phase emerges, and then a three-fold enhancement in the transition temperature ($T_{\mathrm{c}}$) happens. Analyses of the crystal structure and theoretical calculations suggest a pressure-mediated switch of the conduction channel from the $a$- to the $b$-axis occur, followed by a dimensional crossover of conductivity and the Fermi surface from 2D to 3D.
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Submitted 3 May, 2022; v1 submitted 19 October, 2021;
originally announced October 2021.
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Abnormal behavior of Cs polyoxides under high pressure
Authors:
Yuanhui Sun,
Dalar Khodagholian,
Peter Müller,
Cheng Ji,
Huiyang Gou,
Richard Dronskowski,
Maosheng Miao
Abstract:
High-pressure can transform the structures and compositions of materials either by changing the relative strengths of bonds or by altering the oxidation states of atoms. Both effects cause unconventional compositions in novel compounds that have been synthesized or predicted in large numbers in the past decade. What naturally follows is a question: what if pressure imposes strong effects on both c…
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High-pressure can transform the structures and compositions of materials either by changing the relative strengths of bonds or by altering the oxidation states of atoms. Both effects cause unconventional compositions in novel compounds that have been synthesized or predicted in large numbers in the past decade. What naturally follows is a question: what if pressure imposes strong effects on both chemical bonds and atomic orbitals in the same material. A systematic DFT and crystal structure search study of Cs polyoxides under high pressure shows a striking transition of chemistry due to the activation of the Cs 5p core electrons. Opposing to the general trend of polyoxides, the O-O bonds disappear in Cs polyoxides and Cs and O atoms form molecules and monolayers with strong Cs-O covalent bonds. Especially, the abnormal transition of structure and chemical bonds happens to CsO, a solid peroxide that is stable under ambient pressure, at 221 GPa, which can be accessed by current high-pressure experiments.
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Submitted 15 October, 2021;
originally announced October 2021.
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Site-selective magnetic moment collapse in compressed Fe5O6
Authors:
Qiao-Ying Qin,
Ai-Qin Yang,
Xiang-Ru Tao,
Liu-Xiang Yang,
Hui-Yang Gou,
Peng Zhang
Abstract:
Iron oxide is one of the most important components in Earth's mantle. Recent discovery of the stable presence of Fe5O6 at Earth's mantle environment stimulates significant interests in the understanding of this new category of iron oxides. In this paper, we report the electronic structure and magnetic properties of Fe5O6 calculated by the density functional theory plus dynamic mean field theory (D…
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Iron oxide is one of the most important components in Earth's mantle. Recent discovery of the stable presence of Fe5O6 at Earth's mantle environment stimulates significant interests in the understanding of this new category of iron oxides. In this paper, we report the electronic structure and magnetic properties of Fe5O6 calculated by the density functional theory plus dynamic mean field theory (DFT+DMFT) approach. Our calculations indicate that Fe5O6 is a conductor at the ambient pressure with dominant Fe-3d density of states at the Fermi level. The magnetic moments of iron atoms at three non-equivalent crystallographic sites in Fe5O6 collapse at significantly different rate under pressure. Such site-selective collapse of magnetic moments originates from the shifting of energy levels and the consequent charge transfer among the Fe-3d orbits when Fe5O6 is being compressed. Our simulations suggest that there could be high conductivity and volume contraction in Fe5O6 at high pressure, which may induce anomalous features in seismic velocity, energy exchange, and mass distribution at the deep interior of Earth.
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Submitted 10 August, 2021;
originally announced August 2021.
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Pressure-induced Topological and Structural Phase Transitions in an Antiferromagnetic Topological Insulator
Authors:
Cuiying Pei,
Yunyouyou Xia,
Jiazhen Wu,
Yi Zhao,
Lingling Gao,
Tianping Ying,
Bo Gao,
Nana Li,
Wenge Yang,
Dongzhou Zhang,
Huiyang Gou,
Yulin Chen,
Hideo Hosono,
Gang Li,
Yanpeng Qi
Abstract:
Recently, natural van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states. In this work, we systematically investigate both the structural and electronic responses of MnBi2Te4 and MnBi4Te7 to external pressure. In addition to the suppression of antiferromagnetic…
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Recently, natural van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states. In this work, we systematically investigate both the structural and electronic responses of MnBi2Te4 and MnBi4Te7 to external pressure. In addition to the suppression of antiferromagnetic order, MnBi2Te4 is found to undergo a metal-semiconductor-metal transition upon compression. The resistivity of MnBi4Te7 changes dramatically under high pressure and a non-monotonic evolution of \r{ho}(T) is observed. The nontrivial topology is proved to persists before the structural phase transition observed in the high-pressure regime. We find that the bulk and surface states respond differently to pressure, which is consistent with the non-monotonic change of the resistivity. Interestingly, a pressure-induced amorphous state is observed in MnBi2Te4, while two high pressure phase transitions are revealed in MnBi4Te7. Our combined theoretical and experimental research establishes MnBi2Te4 and MnBi4Te7 as highly tunable magnetic topological insulators, in which phase transitions and new ground states emerge upon compression.
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Submitted 16 May, 2020;
originally announced May 2020.
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Diffusion-controlled Alloying of Single-phase Multi-principal Covalent Transition Metal Carbides with Enhanced Damage tolerance and Exceptional Thermal Properties
Authors:
Chong Peng,
Xiang Gao,
Mingzhi Wang,
Lailei Wu,
Hu Tang,
Xiaoming Li,
Qian Zhang,
Yang Ren,
Fuxiang Zhang,
Yuhui Wang,
Bing Zhang,
Bo Gao,
Qin Zou,
Yucheng Zhao,
Qian Yang,
Dongxia Tian,
Hong Xiao,
Huiyang Gou,
Wenge Yang,
Xuedong Bai,
Wendy L. Mao,
Ho-kwang Mao
Abstract:
Multicomponent alloying has displayed extraordinary potential for producing exceptional structural and functional materials. However, the synthesis of single-phase, multi-principal covalent compounds remains a challenge. Here we present a diffusion-controlled alloying strategy for the successful realization of covalent multi-principal transition metal carbides (MPTMCs) with a single face-centered…
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Multicomponent alloying has displayed extraordinary potential for producing exceptional structural and functional materials. However, the synthesis of single-phase, multi-principal covalent compounds remains a challenge. Here we present a diffusion-controlled alloying strategy for the successful realization of covalent multi-principal transition metal carbides (MPTMCs) with a single face-centered cubic (FCC) phase. The increased interfacial diffusion promoted by the addition of a nonstoichiometric compound leads to rapid formation of the new single phase at much lower sintering temperature. Direct atomic-level observations via scanning transmission electron microscopy demonstrate that MPTMCs are composed of a single phase with a random distribution of all cations, which holds the key to the unique combinations of improved fracture toughness, superior Vickers hardness, and extremely lower thermal diffusivity achieved in MPTMCs. The present discovery provides a promising approach toward the design and synthesis of next-generation high-performance materials.
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Submitted 2 September, 2018;
originally announced October 2018.
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Exotic stable calcium carbides: theory and experiment
Authors:
Yan-Ling Li,
Sheng-Nan Wang,
Artem R. Oganov,
Huiyang Gou,
Jesse S. Smith,
Timothy A. Strobel
Abstract:
It is well known that pressure causes profound changes in the properties of atoms and chemical bonding, leading to the formation of many unusual materials. Here we systematically explore all stable calcium carbides at pressures from ambient to 100 GPa using variable-composition evolutionary structure predictions. We find that Ca5C2, Ca2C, Ca3C2, CaC, Ca2C3, and CaC2 have stability fields on the ph…
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It is well known that pressure causes profound changes in the properties of atoms and chemical bonding, leading to the formation of many unusual materials. Here we systematically explore all stable calcium carbides at pressures from ambient to 100 GPa using variable-composition evolutionary structure predictions. We find that Ca5C2, Ca2C, Ca3C2, CaC, Ca2C3, and CaC2 have stability fields on the phase diagram. Among these, Ca2C and Ca2C3 are successfully synthesized for the first time via high-pressure experiments with excellent structural correspondence to theoretical predictions. Of particular significance are the base-centered monoclinic phase (space group C2/m) of Ca2C, a quasi-two-dimensional metal with layers of negatively charged calcium atoms, and the primitive monoclinic phase (space group P21/c) of CaC with zigzag C4 groups. Interestingly, strong interstitial charge localization is found in the structure of R-3m-Ca5C2 with semimetallic behaviour.
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Submitted 20 March, 2015; v1 submitted 23 February, 2015;
originally announced February 2015.
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Novel non-magnetic hard boride Co5B16 synthesized under high pressure
Authors:
Elena Bykova,
Alexander A. Tsirlin,
Huiyang Gou,
Leonid Dubrovinsky,
Natalia Dubrovinskaia
Abstract:
A first cobalt boride with the Co:B ratio below 1:1, Co5B16, was synthesized under high-pressure high-temperature conditions. It has a unique orthorhombic structure (space group Pmma, a = 19.1736(12), b = 2.9329(1), and c = 5.4886(2) Å, R1 (all data) = 0.037). The material is hard, paramagnetic, with a weak temperature dependence of magnetic susceptibility.
A first cobalt boride with the Co:B ratio below 1:1, Co5B16, was synthesized under high-pressure high-temperature conditions. It has a unique orthorhombic structure (space group Pmma, a = 19.1736(12), b = 2.9329(1), and c = 5.4886(2) Å, R1 (all data) = 0.037). The material is hard, paramagnetic, with a weak temperature dependence of magnetic susceptibility.
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Submitted 9 April, 2014;
originally announced April 2014.
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Peierls distortion, magnetism, and high hardness of manganese tetraboride
Authors:
Huiyang Gou,
Alexander A. Tsirlin,
Elena Bykova,
Artem M. Abakumov,
Gustaaf Van Tendeloo,
Asta Richter,
Sergey V. Ovsyannikov,
Alexander V. Kurnosov,
Dmytro M. Trots,
Zuzana Konôpková,
Hans-Peter Liermann,
Leonid Dubrovinsky,
Natalia Dubrovinskaia
Abstract:
We report crystal structure, electronic structure, and magnetism of manganese tetraboride, MnB4, synthesized under high-pressure high-temperature conditions. In contrast to superconducting FeB4 and metallic CrB4, which are both orthorhombic, MnB4 features a monoclinic crystal structure. Its lower symmetry originates from a Peierls distortion of the Mn chains. This distortion nearly opens the gap a…
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We report crystal structure, electronic structure, and magnetism of manganese tetraboride, MnB4, synthesized under high-pressure high-temperature conditions. In contrast to superconducting FeB4 and metallic CrB4, which are both orthorhombic, MnB4 features a monoclinic crystal structure. Its lower symmetry originates from a Peierls distortion of the Mn chains. This distortion nearly opens the gap at the Fermi level, but despite the strong dimerization and the proximity of MnB4 to the insulating state, we find indications for a sizable paramagnetic effective moment of about 1.7 muB/f.u., ferromagnetic spin correlations and, even more surprisingly, a prominent electronic contribution to the specific heat. However, no magnetic order has been observed in standard thermodynamic measurements down to 2 K. Altogether, this renders MnB4 a structurally simple but microscopically enigmatic material; we argue that its properties may be influenced by electronic correlations.
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Submitted 25 December, 2013;
originally announced December 2013.
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Discovery of a superhard iron tetraboride superconductor
Authors:
Huiyang Gou,
Natalia Dubrovinskaia,
Elena Bykova,
Alexander A. Tsirlin,
Deepa Kasinathan,
Asta Richter,
Marco Merlini,
Michael Hanfland,
Artem M. Abakumov,
Dmitry Batuk,
Gustaaf Van Tendeloo,
Yoichi Nakajima,
Aleksey N. Kolmogorov,
Leonid Dubrovinsky
Abstract:
Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride FeB4 were synthesised at pressures above 8 GPa and high temperatures. Magnetic susceptibility measurements demonstrated bulk superconductivity below 2.9 K. The putative isotope effect on the superconducting critical temperature indicates that FeB4 is likely a phonon-mediated superconductor, which is unexpected in the light o…
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Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride FeB4 were synthesised at pressures above 8 GPa and high temperatures. Magnetic susceptibility measurements demonstrated bulk superconductivity below 2.9 K. The putative isotope effect on the superconducting critical temperature indicates that FeB4 is likely a phonon-mediated superconductor, which is unexpected in the light of previous knowledge on Fe-based superconductors. The discovered iron tetraboride is highly incompressible and has the nanoindentation hardness of 65(5) GPa, thus, it opens a new class of highly desirable materials combining advanced mechanical properties and superconductivity.
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Submitted 18 April, 2013;
originally announced April 2013.