Strongly Correlated Superconductivity (SCS)

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Our research interest is to study the low temperature novel physics when the strongly correlated superconductor is tuned through a quantum critical point by pressure, magnetic field or doping.

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1. Iron-based superconductor

Pressure tuned superconductivity and normal state behavior in Ba(Fe0.943Co0.057)2As2

A quantum critical point (QCP) is the point of transitionbetween two stable phases at absolute zero temperature driven by quantumfluctuations. A QCP can be achieved by tuning a magnetic order to a zerotemperature transition by applying pressure, magnetic field or chemical doping.In iron-based superconductors, it is a matter of debate in iron-basedsuperconductors whether a QCP is hidden inside the superconducting dome. Controversialresults are obtained, for example, a sharp peak of the zero-temperaturepenetration depth at optimal composition is observed in BaFe2(As1-xPx)2,suggesting the existence of a QCP at x = 0.3. While neutron scatteringmeasurements on Ba(Fe1-xNix)2As2observed a first-order-like antiferromagnetism to superconductivity transition,suggests the absence of a quantum critical point.

In this work, we probe the phase diagram of Ba(Fe_1-xCo_x)₂As₂ closeto the antiferromagnetic boundary through measurements of resistivity andmagnetization by tuning the applied pressure in a sample with x = 0.057.Wefound that the resistivity shows a linear temperature dependence around acritical pressure of 3.5 GPa where Tc is maximum. In addition, theresidual resistivity and the resistivity at Tc all change around thesame critical pressure. Furthermore, we detected signs of an accompanied changein the superconducting volume. These results are most likely due to a possiblepressure tuned QCP hidden inside the superconducting dome of Ba(Fe1-xCox)2As2.In addition, we also performed I-V measurements on Ba(Fe1-xCox)2As2with various Co doping. Considerably enhanced flux-flow resistivity ρffwas detected for x = 0.06, perhaps due to enhancement of spin fluctuations nearQCP.

FigureTemperature-pressure (T-P) phase diagram of Ba(Fe_1-xCo_x)₂As₂

Phys. Rev. B 97, 144515 (2018)

Optical study ofDirac fermions in antiferromagnetic compound CaFeAsF

The parentantiferromagnetic phase of the iron-based superconductors has a metalliccharacter and possesses nontrivial topological properties with Dirac fermionsnear to the Fermi energy. The observation of Dirac fermion state with protectedDirac cones in the parent compound of iron-based superconductor provide us anew kind of topological material, after cuprates, graphene, topologicalinsulators and Weyl semimetals.

CaFeAsF is anew member of 1111 family of iron-based superconductor, but with oxygen free.The optical conductivity probes the bulk band structure and carrierelectrodynamics over a broad energy range and provides rich information on theintraband and interband transitions of possible Dirac cones. Recently theavailability of sizable single crystals allows for an optical study of theintrinsic properties of this material.

In the SDWstate of CaFeAsF, we have observed a singular absorption feature and tworegions of quasilinear conductivity that have been interpreted in terms of theresponse of Dirac fermions. Note that such features disappear rapidly as afunction of electron and hole doping in the BaFe2As2system. In addition, we found in CaFeAsF that the infrared-active Fe-As phononmode shows signatures of a strong coupling with the Dirac fermions that appearin the SDW state. Very recently, the existence of Dirac fermions in CaFeAsF hasbeen confirmed by quantum oscillation measurements, Phys. Rev. X 8, 011014(2018).

FigureOptical conductivity of CaFeAsF after subtraction of the Drude and phonon termsin the antiferromagnetic state.

Phys. Rev. B 97, 195110(2018)

Pressure-inducedsuperconductivity in parent CaFeAsF single crystals

CaFeAsF parent compoundexhibits pressure-induced superconductivity and the maximumTc is higher than that inLaFeAsO, making it a promising candidate as a parent compound for high Tc superconductor. However,up to now, the phase diagram of this material is based on data of polycrystalsamples and controversial results are obtained. Here, for the first time, weperformed high pressure resistivity measurements on single crystal sample ofCaFeAsF parent compound up to about 50 GPa and we determined the change ofstructural and magnetic phase transition temperature and the superconductingtemperature with pressure. In strongly contrast to 122 family of iron-basedsuperconductor, the SC of CaFeAsF is quite robust under pressure and shows nodome-shaped behavior, which is coincident with reported monoclinic phase. Thesefindings provide valuable insights to understand the interplay between thestructure and the appearance of SC in iron-based superconductors.

Figure  The pressure-temperature phase diagram ofCaFeAsF.

Phys. Rev. B 97, 174505(2018)

2. Heavy fermionsuperconductor

Universal linear-temperature resistivity: possible quantum diffusiontransport in strongly correlated superconductors

What underlies the linear resistivity in stronglycorrelated superconductors is a well known, intriguing and long-standingquestion in condensed matter physics. Based on the pressure tuned resistivitydata of heavy fermion superconductor CeCoIn5, and combined with datareported on all kinds of superconductors available in the literature, we founda universal relation, which bridges the slope of the linear-T-dependent resistivity (dρ/dT) to the London penetration depth λLat zero temperature. In this work, we investigate nearly 70 differentsuperconductors, including cuprates, pnictides, heavy fermiion superconductors,and conventional metal superconductors as well. The combined data span nearlysix orders of magnitude. This scaling relation holds for cuprate, pnictide andheavy fermion superconductors as well, regardless of the significantdifferences in the strength of electronic correlations, transport directions,and doping levels.

Our analysis suggest the ubiquitous presence of the quantum diffusion in superconductors, whichnot only causes the scaling behavior of linear-temperature resistivity observedin this paper but also is responsible for those well-known scaling relations ofsuperconductors, like Uemura’s law and Homes’ law. The experimental finding ofquantum diffusionin superconductors indicates a fundamental inadequacy of previous understanding of superconductivity.

Figure  Log-log plot of  vs. for various strongly correlated superconductors.

Sci. Rep. 7, 9469 (2017)

Recent Publications

70.S. Yesudhas*, N. Yedukondalu*, M. K. Jana, J. B. Zhang, J. Huang, B. Chen, H. Deng, R. Sereika, H. Xiao, S. Sinogeikin, C. K. Benson, K. Biswas, J. B. Parise, Y. Ding*, and H. K. Mao, “Structural, vibrational and electronic properties of 1D-TlInTe₂ under high pressure: A combined experimental and theoretical study”, Inorganic Chemistry 60, 9320 (2021).

69.H. Deng*, J. Zhang, M. Yong, D. Wang, Q. Hu, S. Zhang, R. Sereika, T. Nakagawa, B. Chen, X. Yin, H. Xiao, X. Hong, J. Ren, M. Han*, J. chang*, H. Weng, Y. Ding*, H. Lin, and H. Mao, “Metallization of quantum material GaTa₄Se₈ at high pressure”, J. Phys. Chem. Lett. 12, 5601 (2021).

68.C. Zhang, T. Hu, T. Wang, Y. F. Wu, A. B. Yu, J. N. Chu, H. Zhang, X. F. Zhang, H. Xiao, W. Peng, Z. F. Di, G. Mu, “Two-dimensional superconductivity in an ultrathin iron-arsenic superconductor”, 2D Material 8, 025024 (2021).

67.Ho-Kwang Mao, Bin Chen, Huiyang Gou, Kuo Li, Jin Liu, Lin Wang, H. Xiao and Wenge Yang, “2020-Transformative Science in the pressure dimension”, Matter and Radiation at Extremes 6, 013001 (2021).

66.M. Y. Li, J. Huang, W. T. Guo, R. Yang, T. Hu, A. B. Yu, Y. L. Huang, M. Zhang*, W. Zhang, J. –M. Zhang*, and H. Xiao^*, “Pressure tuning of iron-based superconductor (Ca_0.73La_0.27)FeAs₂”, Phys. Rev. B 103 024502 (2021).

65.A. B. Yu, Z. Huang, C. Zhang, Y. F. Wu, T. Wang, T. Xie, C. Liu, H. Li, .W. Peng, H. Q. Luo, G. Mu, H. Xiao, L. X. You, T. Hu*, “Study of superconducting anisotropy and vortex pinning in CaKFe4As4 and KCa₂Fe₄As₄F₂”, Chin. Phys. B Vol. 30, 027401 (2021).

64.L. B. Lei, C. Zhang, A. B. Yu, Y. F. Wu, W. Peng. H. Xiao, S. Qiao, T. Hu*, “The transport properties of ultrathin 2H-NbSe₂”, Superconductor Science and Technology 34, 025019 (2021)

63.X. W. Han, Y. F. Wu, H. Xiao, M. Zhang, M. Gao, Y. Liu, J. Wang, T. Hu*, X. M. Xie, and Z. F. Di*, “Disorder-Induced Quantum Griffiths Singularity Revealed in an Artificial 2D superconducting system”, Adv. Sci. 7, 1902849 (2020).

62.Y. L. Huang, R. Yang, P. G. Li*, H. Xiao*, “Anisotropy of Ca_0.73La_0.27(Fe_0.96Co_0.04)As₂ studied by torque magnetometry”, Chin. Phys. B Vol. 29(9), 097405 (2020).

61.Y. F. Wu, A. B. Yu, L. B. Lei, C. Zhang, T. Wang, Y. H. Ma, Z. Huang, L. X. Chen, Y. S. Liu, C. M. Schneider, G. Mu, H. Xiao, and T. Hu*, “Point-contact spectroscopy measurements of superconducting NbN and CaFe_0.88Co_0.12AsF by nano-Au array”, Phys. Rev. B 101, 174502 (2020).

60.H. Xiao*, T. Hu, H. X. Zhou, X. J. Li, S. L. Ni, F. Zhou, and X. L. Dong, “Probing the anisotropy of Li_0.84Fe_0.16OHFE_0.98Se by angular dependent torque measurements”, Phys. Rev. B 101, 184520 (2020).

59. R. Yang, J. W. Huang, N. Zaki, I. Pletikosic, Y. M. Dai, H. Xiao, T. Valla, P. D. Johnson, X. J. Zhou, X. G. Qiu*, and C. C. Homes*, “Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr_0.67Na_0.33Fe₂As₂”, Phys. Rev. B 100, 235132 (2019).

58.A. B. Yu, T. Wang, Y. F. Wu, Z. Huang,H. Xiao, G. Mu, and T. Hu, “Probing superconducting anisotropy of single crystal KCa₂Fe₄As₄F₂ by magnetic torque measurements”, Phys. Rev. B 100, 144505 (2019).

57.W. J. Ban,, D. S. Wu, C. C. Le, J. P. Hu, J. L. Luo, and H. Xiao*, “Optical spectroscopy study of the topological property in PrSb”, Phys. Rev. B 100, 115133 (2019).

56.W. J. Ban, D. S. Wu, B. Xu, J. L. Luo andH. Xiao*, “Revealing ‘plasmaron’ feature in DySb by optical spectroscopy study”, J. Phys.: Condens. Matter 31, 405701 (2019).

55.Gang Mu, Teng Wang, Yonghui Ma, Wei Li, Jianan Chu, Lingling Wang, Jiaxin Feng, H. Xiao, Zhuojun Li, Tao Hu, and Xiaosong Liu, “Two-gap superconductivity in CaFe_0.88Co_0.12AsF revealed by temperature dependence of the lower critical field Hc₁(T)”, njp Quantum Materials 4, 33 (2019).

54.Wu, Yufeng;Xiao, H; Li, Qiao; Li, Xiaojiang; Li, Zhuojun; Mu, Gang; Jiang, Da; Hu, Tao; Xie, Xiaoming, “The transport properties in graphene/single-unit-cell cuprates van der Waals heterostructure”, Superconductor Science and Technology 32 085007 (2019).

53. J. Huang, C. Zhang, Y. H. Ma, T. Wang, G. Mu, L. Yu, T. Hu, and H. Xiao*, “Pressure effect on iron-based superconductor CaFe_0.88Co_0.12AsF”, J. Phys. Condens. Matter 31, 325602 (2019).

52. R. Yang, Y. M. Dai, J. Yu, Q. T. Sui, Y. Q. Cai, Z. A. Ren, J. Hwang, H. Xiao, X. Zhou, X. G. Qiu, and C. C. Homes, “Unravelling the mechanism of semiconducting-like behavior and its relation to superconductivity in (CaFe_1-xPt_xAs)10Pt₃As₈”, Phys. Rev. B 99, 144520 (2019).

51.Jianbo Zhang, Dayu Yan, Sorb Yesudhas, Hongshan Deng, H. Xiao, Bijuan Chen, Raimundas Sereika, Xia Yin, Changjiang Yi, Youguo Shi, Zhenxian Liu, Ekaterina M. Parschke, Cheng-Chien Chen, Jun Chang, Yang Ding and Ho-Kwang Mao, “Lattice frustration in spin-orbit Mott insulator Sr₃Ir₂O₇ at high pressure”, njp Quantum Materials 4, 23 (2019).

50.Chong Peng, Xiang Gao, M. Z. Wang, L. L. Wu, Hu Tang, X. Li, Qian Zhang, Y. Ren, F. X. Zhang,  Y. H. Wang, B. Zhang, Bo Gao, Q. Zou, Y. C. Zhao, Q. Yang, D. X. Tian, Hong Xiao, Huiyang Gou, Wenge Yang, X. D. Bai, W. D. Mao, and Ho-Kwang Mao, “Diffusion-controlled alloying of single-phase multi-principal transition metal carbides with high toughness and low thermal diffusivity”,  Appl. Phys. Lett. 114, 011905 (2019).

49. Hu Tang, Biao Wan, Bo Gao, Y. Muraba, Qin Qin, Bingmin Yan, P. Chen, Qingyang Hu, D. Zhang, L. Wu, M. Wang, H. Xiao, Huiyang Gou, F. Gao, Ho-Kwang Mao, and H. Hosono, “Metal-to-semiconductor transition and electronic dimensionality reduction of Ca₂N electride under pressure”, Adv. Sci. 5, 1800666 (2018).

48. X. Yin, C. Zhang, G. Mu, T. Hu, M. Zhang, and H. Xiao*, "Pressure tuning of iron-based superconductor  Ca₁₀(Pt₃As₈)((Fe_0.95)₂As₂)₅”, J. Phys. Condens. Matter 31 145201 (2019).

47. S. Radmanesh, C. Martin, Y. Zhu, X. Yin, H. Xiao, Z. Mao and L. Spinu, "Evidence for unconventional superconductivity in half-Heusler YPdBi and TbPdBi compounds revealed by London penetration depth measurements", Phys. Rev. B 98, 241111 (2018).

46. W. J. Ban, B. Xu, W. H. Li, Y. Wang, J. J. Ge, P. G. Li, R. Yang, Y. M. Dai, Z. Q. Mao, and H. Xiao^* , "Revealing the pseudogap in Sr₃(Ru_0.985 Fe _0.015)₂O₇ by optical spectroscopy", Phys. Rev. B 98, 205111 (2018).

45. H. Xiao^*, T. Hu, W. Liu, Y. L. Zhu, P. G. Li, G. Mu, T. Hu, and Z. Q. Mao, “Superconductivity in half-Heusler compound TbPdBi”, Phys. Rev. B 97, 224511 (2018).

44. Yinbo Sun, H. Xiao,  Miao Zhang, Zhongying Xue, Yongfeng Mei, Xiaoming Xie, Tao Hu, Zengfeng Di, and Xi Wang, “Double quantum criticality in superconducting tin-arrays/graphene hybrid”, Nat. Commun.9 2159 (2018).

43. B. Xu, H.Xiao*, B. Gao, Y. H. Ma, G. Mu, P. Marsk, E. Sheveleva, F. Lyzwa, Y. M.Dai, R. P. S. M. Lobo, and C. Bernhard, “Opticalstudy of Dirac fermions and related phonon anomalies in antiferromagneticcompound CaFeAsF”, Phys. Rev. B 97, 195110 (2018).

42. Bo Gao, Yonghui Ma, Gang Mu and H Xiao*, “Pressure-induced superconductivity in parent CaFeAsF single crystals”, Phys.Rev. B 97, 174505 (2018).

41. W. Liu, Y. F. Wu, X. J. Li, S. L. Budko, P.C. Canfield, C. Panagopoulos, P. G. Li, G. Mu, T. Hu, C. C. Almasan, and H. Xiao*, “Pressure tuned superconductivity and normal state behavior in Ba(Fe_0.943Co_0.057)₂As₂”,Phys.Rev. B 97, 144515 (2018).

40. B. Xu,Y.M. Dai,  L.X. Zhao,  K.Wang,R. Yang,W.Zhang,J. Y. Liu, H. Xiao,G.F. Chen, S. A. Trugman, J. –X. Zhu,  A.J. Taylor,  D. A. Yarotske, R. P.Prasankumar, and X. G. Qiu, “Temperature-tunable Fanoresonance induced by strong coupling between Weyl fermions and phonons in TaAs”, Nat. Commun. 8:14933(2017).

39. X. Y. Huang, D. J. Haney, Y. P.Singh, T. Hu, H. Xiao, Hai-HuWen, M. Dzero, and C. C. Almasan, ”Universality and unconventional enhancement of flux-flow resistivity in Ba(Fe_1-xCo_x)₂As₂“,Phys.Rev. B 95, 184513 (2017).

38. TaoHu, Yinshang Liu, Hong Xiao*,Gang Mu, and Yi-feng Yang, “Universal linear-temperatureresistivity: possible quantum diffusion transport in strongly correlatedsuperconductors”, Sci. Rep. 7, 9469 (2017).

37. X. Y. Huang, Y. P. Singh, D. J.Haney, T. Hu, H. Xiao, Hai-HuWen, Shuai Zhang, M. Dzero, and C. C. Almasan, “Relationship between critical current and flux-flow resistivity in themixed state of Ba(Fe_1-xCo_x)₂As₂”,  Phys. Rev. B 96,094509 (2017).

36. H. Xiao*,B. Gao, Y. H. Ma, X. J. Li, G. Mu and T. Hu, “Angular dependent torque measurements on CaFe_0.88Co_0.12AsF”,J. Phys. Condens. Matter 28, 325701 (2016)

35. H. Xiao*,B. Gao, Y. H. Ma, X. J. Li, G. Mu and T. Hu, “Superconducting fluctuation effect in CaFe_0.88Co_0.12AsF”, J. Phys. Condens. Mater 28, 455701 (2016)

34. B.Xu, Y. M. Dai,H. Xiao, B.Shen, Z. R. Ye, A. Forget, D. Colson, D. L. Feng, H. H. Wen, X. G. Qiu, and R. P. S. M. Lobo, “Optical observation of spin-density-wave fluctuations in Ba122iron-based superconductors”,  Phys. Rev. B 94, 085147 (2016)

33. B. Xu, Y. M. Dai, L. X. Zhao, K.Wang, R. Yang, W. Zhang, J. Y. Liu,H.Xiao, G. F. Chen, A. J. Taylor, D. A. Yarotski, R. P. Prasankumar, andX. G. Qiu, “Optical spectroscopy of theWeyl semimetal TaAs”, Phys. Rev. B(R) 93,121110 (2016)

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