Prediction and description of a chiral pseudogap phase

Abstract

We point out that a system which supports chiral superconductivity should also support a chiral pseudogap phase: a finite temperature phase wherein superconductivity is lost but time reversal symmetry is still broken. This chiral pseudogap phase can be viewed as a state with phase incoherent Cooper pairs of a definite angular momentum. This physical picture suggests that the chiral pseudogap phase should have definite magnetization, should exhibit a (non-quantized) charge Hall effect, and should possess protected edge states that lead to a quantized thermal Hall response. We explain how these phenomena are realized in a Ginzburg-Landau description, and comment on the experimental signatures of the chiral pseudogap phase. We expect this work to be relevant for all systems that exhibit chiral superconductivity, including doped graphene and strontium ruthenate.Chiral superconductors feature pairing gaps that wind in phase around the Fermi surface (FS), breaking time reversal symmetry (TRS) [1][2][3][4]. They realize topological superconductivity [5][6][7][8] and exhibit a host of fascinating and technologically useful properties, such as protected edge states, a quantized thermal Hall effect, and unconventional zero modes in vortices [1][2][3][4]. Chiral pwave superconductivity is believed to have been found in strontium ruthenate [9], and chiral d wave superconductivity has been established to be the leading weak coupling instability in strongly doped graphene [10,11]. However, all theoretical work to date has focused on chiral superconductors at low temperatures. In this work, we argue that much of the exotic phenomenology associated with chiral superconductivity can be exhibited even at high temperatures, when the superconductivity is absent. In particular, we predict the existence of a chiral pseudogap phase with a rich phenomenology, including a magnetic dipole moment, non-quantized charge Hall effect, protected edge states, and quantized thermal Hall effect. Since this pseudogap phase does not require low temperatures or exceptionally clean systems (unlike chiral superconductivity), we expect it to be advantageous for nanoscience applications.Emery and Kivelson have pointed out that phase incoherent Cooper pairs can form at temperatures much higher than the characteristic temparature for onset of superconductivity [12]. This 'preformed Cooper pairs' picture has been invoked as a possible explanation for the pseudogap phase of the cuprate high-T c materials. The nature of the pseudogap phase of the cuprates remains controversial, not least because the pre-formed Cooper pairs picture for the cuprates does not lead to many sharp testable predictions. However, the situation is markedly different for a chiral superconductor, where a pseudo-gap phase with phase incoherent pre-formed Cooper pairs can still break time reversal symmetry. The resulting chiral pseudo-gap phase has a rich and distinctive phenomenology, which should be readily testable experimentally.In this letter, we provide a Ginzburg-Landau descriptio...

Orthogonal metal in the Hubbard model with liberated slave spins

“…Therefore, and given the absence of f -fermion interactions that could produce such a gap in their models, it is surprising that systems with uncondensed pairs of fermions are suggested as candidates for OMs in Ref. [31]. In contrast, our work appears to provide a faithful realization of the fermionic OM deduced from mean-field theory.…”

“…8 the momentum distribution function (36) and the local Green function defined in Eq. (31), which depend only on |U |. We take U = 6, close to the maximum of T Q ≈ 0.1 in Fig By adding a small magnetic field h Q for theQ i or, equivalently, a small Hubbard interaction of U = h Q [cf.…”

“…Of particular interest for our work is the observation of Ref. [31] that-beyond single-site meanfield theories-the gapped phase of the slave spins is not a Mott insulator but a fractionalized orthogonal metal (OM, see Sec. V A for more details).…”

“…V A for more details). OMs are characterized by a gap for single-particle excitations but gapless transport and may be considered the simplest example of non-FLs [31]. They provide a framework to reconcile the absence of quasiparticle excitations in ARPES with the presence of a Fermi surface in quantum oscillation measurements [32].…”

Fluctuation and strain effects in a chiralp-wave superconductor

“…Moreover, as a chiral superconducting state not only breaks U (1) symmetry, but also Z 2 (TRS), fluctuations associated to the latter possibly lead to a non-superconducting TRS-breaking phase at temperatures above the superconducting T c . 4,5 Such behavior has also been found for multi-band superconductors with frustrated interband coupling 6,7 and is sometimes referred to as having a "preemptive" 8 or "vestigial" 9 phase. Alternatively, the fluctuations can also drive the transition to be (weakly) first order.…”