Electron Correlation and Pairing States in Superconductors without Inversion Symmetry

Fujimoto, Satoshi

doi:10.1143/jpsj.76.051008

Cited by 220 publications

(226 citation statements)

References 48 publications

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“…18,19,20 In these superconductors, the admixture of even-and odd-parity pairings has been suggested theoretically. 21,22,23,24 Thus, we expect the mixing of parity also occurs in the present system. In this case, the change in the pairing symmetry under applied voltage is not a phase transition but a crossover between different parities.…”

supporting

confidence: 50%

Electrically controlled superconducting states at the heterointerfaceSrTiO3/LaAlO3

et al. 2009

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We study the symmetry of Cooper pair in a two-dimensional Hubbard model with the Rashbatype spin-orbit interaction as a minimal model of electron gas generated at a heterointerface of SrTiO3/LaAlO3. Solving theÉliashberg equation based on the third-order perturbation theory, we find that the gap function consists of the mixing of the spin-singlet dxy-wave component and the spin-triplet (px ± ipy)-wave one due to the broken inversion symmetry originating from the Rashbatype spin-orbit interaction. The ratio of the d-wave and the p-wave component continuously changes with the carrier concentration. We propose that the pairing symmetry is controlled by tuning the gate voltage.PACS numbers: 74.25.Dw, 74.78.Fk, 71.10.Fd Recent development of technology of epitaxial growth makes it possible to fabricate heterointerface between two different transition-metal oxides. 1,2 The discovery of the generation of two-dimensional electron gas (2DEG) at the n-type heterointerface SrTiO 3 /LaAlO 3 attracts much interest 3 since both SrTiO 3 and LaAlO 3 are band insulators in the bulk material. It is also noted that this 2DEG shows superconductivity with transition temperature T c = 200 mK. 4 This superconductivity differs from the superconductivity of bulk SrTiO 3 with T c = 300 mK in the carrier concentration and the dimensionality of mobile electrons. 5 The discovery of superconductivity is significant since it is promising to control the superconducting states electrically by the applied voltage. Controlling the number of carrier by applied voltage in superconductors is one of the intriguing issues to understand the mechanism of the superconductivity. In cuprates, a superconducting region is located next to an antiferromagnetic phase in an n-T phase diagram. However, in cuprate superconductors, it is not easy to tune the number of carrier by external fields such as the magnetic field or the gate voltage since the number of carrier depends on material compositions. On the other hand, the carrier number of 2DEG at the heterointerface SrTiO 3 /LaAlO 3 can be tuned by the gate voltage since the carrier is generated by the polar and unpolar nature of LaAlO 3 and SrTiO 3 , respectively. 6 Actually, electrostatically tuned superconductor-metal-insulator transition was found to be accessible. 7,8,9 When the electron correlations (Coulomb interaction) are responsible to the superconductivity, the pairing symmetry depends on the number of carrier: The spin-triplet p-wave pairing is favored at low density, 10,11,12,13,14 while on the other hand, the spin-singlet d x 2 −y 2 -wave pairing is favored near half filling. 15,16 Thus, at the heterointerface of oxides with large Coulomb interaction, the phase transition between the spin-singlet and spin-triplet states can be observed by the applied voltage.Another characteristic feature at the heterointerface is lack of the inversion symmetry along the direction perpendicular to the interface (z-axis), which induces the asymmetric spin-orbit interaction called the Rashbatype spin-orbit intera...

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confidence: 50%

Electrically controlled superconducting states at the heterointerfaceSrTiO3/LaAlO3

et al. 2009

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“…Several theoretical approaches have been developed to try to understand this superconductor [15,16,17,18,19]. The models take into account the splitting of the spin-degenerate bands caused by the absence of inversion symmetry.…”

Section: Superconducting Statementioning

confidence: 99%

Non-centrosymmetric Heavy-Fermion Superconductors

Kimura

Bonalde

2012

Non-Centrosymmetric Superconductors

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In this chapter we discuss the physical properties of a particular family of non-centrosymmetric superconductors belonging to the class heavy-fermion compounds. This group includes the ferromagnet UIr and the antiferromagnets CeRhSi 3 , CeIrSi 3 , CeCoGe 3 , CeIrGe 3 and CePt 3 Si, of which all but CePt 3 Si become superconducting only under pressure. Each of these superconductors has intriguing and interesting properties. We first analyze CePt 3 Si, then review CeRhSi 3 , CeIrSi 3 , CeCoGe 3 and CeIrGe 3 , which are very similar to each other in their magnetic and electrical properties, and finally discuss UIr. For each material we discuss the crystal structure, magnetic order, occurrence of superconductivity, phase diagram, characteristic parameters, superconducting properties and pairing states. We present an overview of the similarities and differences between all these six compounds at the end. CePt 3 SiThe enormous interest in superconductors without inversion symmetry started with the discovery of superconductivity in the heavy-fermion compound CePt 3 Si [1], which exhibits long-range antiferromagnetic (AFM) order below the Neel temperature T N = 2.2 K and becomes superconducting at the critical temperature T c = 0.75 K. CePt 3 Si is the only known heavy-fermion (HF) compound without inversion symmetry that superconducts at ambient pressure, as opposed to the cases of CeIrSi 3 , CeRhSi 3 , CeCoGe 3 , CeIrGe 3 and UIr. The heavy-fermion character has

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“…2,3 However, if the crystal structure does not have an inversion center (noncentrosymmetric), this removes the parity constraint on the Cooper pair classification and allows for an admixture of spin-singlet and spin-triplet pairing into a mixed-parity pairing state. [4][5][6][7][8] In noncentrosymmetric (NCS) superconductors, an asymmetric potential gradient yields an antisymmetric spin-orbit coupling (ASOC), which breaks the spin degeneracy and splits the Fermi surface in two by spin orientation. 6,7 This unusual pairing and tunability by the strength of the ASOC can manifest itself in unconventional superconducting behavior, such as a nodal superconducting energy gap, and therefore NSC superconductors are good materials to explore exotic superconducting properties.…”

Section: Introductionmentioning

confidence: 99%

“…[4][5][6][7][8] In noncentrosymmetric (NCS) superconductors, an asymmetric potential gradient yields an antisymmetric spin-orbit coupling (ASOC), which breaks the spin degeneracy and splits the Fermi surface in two by spin orientation. 6,7 This unusual pairing and tunability by the strength of the ASOC can manifest itself in unconventional superconducting behavior, such as a nodal superconducting energy gap, and therefore NSC superconductors are good materials to explore exotic superconducting properties. 9,10 Research interest into NCS superconductors expanded significantly after the discovery of unconventional superconductivity in CePt3Si, 11 along with other heavy fermion (HF) compounds such as UIr, CeRhSi3 and CeIrSi3.…”

Section: Introductionmentioning

confidence: 99%

Tuning of superconductivity by Ni substitution into noncentrosymmetric ThCo1−xNixC2

et al. 2017

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The recently discovered noncentrosymmetric superconductor ThCoC2 was observed to show unusual superconducting behavior with a critical temperature of Tc=2.65K. Here we investigate the effect of Nickel substitution on the superconducting state in ThCo1-xNixC2. Magnetization, resistivity, and heat capacity measurements demonstrates Ni substitution has a dramatic effect with critical temperature increased up to Tc=12.1K for x=0.4 Ni concentration, which is a rather high transition temperature for a noncentrosymmetric superconductor. In addition, the unusual superconducting characteristics observed in pure ThCoC2 appear to be suppressed or tuned with Ni substitution towards a more conventional fully gapped superconductor.

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Electron Correlation and Pairing States in Superconductors without Inversion Symmetry

Cited by 220 publications

References 48 publications

Electrically controlled superconducting states at the heterointerfaceSrTiO3/LaAlO3

Electrically controlled superconducting states at the heterointerfaceSrTiO3/LaAlO3

Non-centrosymmetric Heavy-Fermion Superconductors

Tuning of superconductivity by Ni substitution into noncentrosymmetric ThCo1−xNixC2

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