Research Progress

Temperature and angular dependence of the upper critical field in K2Cr3As3

author: time:2017-01-04 clicks:

The out-of-plane Hc2(θ) at various temperatures for K2Cr3As3. The solid lines and the dashed pink curve (for the 5K data only) are the fitted data using orbit limited Hc2 including angle-dependence of Pauli limit and only orbit limit, respectively. Polar plot of the extracted Hc2(φ). The red (blue) triangles come from the rotation of the derived data withφr= 120◦(−120◦), respectively.

(Phys. Rev. B 119, 056601(2017))

Background

Recently, superconductivity was discovered in a Cr-based family A2Cr3As3 (A=K, Rb, and Cs) which possess a quasi-one-dimensional (quasi-1D) crystal structure characterized by infinite [(Cr3As3)2−]linear chains, called double-walled subnanotubes, which are separated byalkali-metal cations. Unconventional SC in K2Cr3As3 or Rb2Cr3As3 has been supported by accumulating experimental and theoretical results from the Sommerfeld specific-heat coefficient, a large upper critical field, the nuclear quadrapole resonance, penetration-depth measurement, band-structure calculations and also the expected Tc suppression.


What we discover?

We report measurements of the upper critical field Hc2 as functions of temperature T , polar angleθ(of the field direction with respect to the crystallographic c axis), and azimuthal angleφ(of the field direction relative to the a axis within the ab plane). We confirm that the anisotropy in Hc2(T) becomes inverse with decreasing temperature. At low temperatures, Hc2(θ) data are featured by two maxima atθ= 0 (H _ c) andπ/2 (H⊥c), which can be quantitatively understood only if uniaxial effective-mass anisotropy and absence of Pauli paramagnetic effect for H⊥c are taken simultaneously into consideration. The in-plane Hc2(φ) profile shows a unique threefold modulation especially at low temperatures. Overall, the characteristics of the Hc2(θ,φ,T ) data mostly resemble those of the heavy-fermion superconductor UPt3, and we argue in favor of a dominant spin-triplet superconductivity with odd parity in K2Cr3As3.


Why is this important?

Spin-triplet superconductivity is rare, and it contains rich and interesting physics which in turn help us to build up a full and deep understanding of superconductivity. K2Cr3As3is a newly discovered superconductor featured by significant electron correlations as well as a quasi-one-dimensional and non-centrosymmetric crystal structure. Previous theoretical and experimental studies on this material show some signatures of spin-triplet superconductivity, but no decisive evidence has been given so far. The solid evidence of a triplet superconductivity inK2Cr3As3shown here will certainly have significant impact in the area of superconductivity. It will also attract attention from the communities of the low-dimension system and strongly correlated electron systems.


Why did they need WHMFC?

The upper critical field ofK2Cr3As3is high. In order to measure the Hc2, we employ the pulsed magnetic field to suppress its superconductivity. The material is extremely air-sensitive. While the center also has a glove-box, enabling sample in inert gas during the whole experimental procedure.


Who did the research?

Zuakun Zuo,1Jin-Ke Bao,2Yi Liu,2Jinhua Wang,1Zhao Jin,1Zhengcai Xia,1Liang Li,1Zhuan Xu,2,3Jian Kang,4Zengwei Zhu,1,*and Guang-Han Cao2,3, †

1.Wuhan National High Magnetic Field Center, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China

2. Department of Physics, Zhejiang University, Hangzhou 310027, China

3. Collaborative Innovation Centre of Advanced Microstructures, Nanjing 210093, China

4. School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA


Funding:

J.K. is supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. de-sc0012336. Z.Z. is supported by the 1000 Youth Talents Plan, the National Science Foundation of China (Grant No. 11574097) and The National Key Research and Development Program of China (Grant No. 2016YFA0401704). G.-H.C. is supported by National Key R & D Program of the MOST of China (Grant No. 2016YFA0300202) and the National Science Foundation of China (Grant No. 11674281).

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