| 1. |
- Bonetti, Pietro M., et al.
(author)
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Interaction-driven first-order and higher-order topological superconductivity
- 2024
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:18
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Journal article (peer-reviewed)abstract
- We investigate topological superconductivity in the Rashba-Hubbard model, describing heavy-atom superlattice and van der Waals materials with broken inversion. We focus in particular on fillings close to the van Hove singularities, where a large density of states enhances the superconducting transition temperature. To determine the topology of the superconducting gaps and to analyze the stability of their surface states in the presence of disorder and residual interactions, we employ an fRG+MFT approach, which combines the unbiased functional renormalization group (fRG) with a real-space mean-field theory (MFT). Our approach uncovers a cascade of topological superconducting states, including ?1 and ?1 pairings, whose wave functions are of dominant ?- and ?-wave character, respectively, as well as a time-reversal breaking ?1+??1 pairing. While the ?1 and ?1 states have first-order topology with helical and flat-band Majorana edge states, respectively, the ?1+??1 pairing exhibits second-order topology with Majorana corner modes. We investigate the disorder stability of the bulk superconducting states, analyze interaction-induced instabilities of the edge states, and discuss implications for experimental systems.
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| 2. |
- Chakraborty, Debmalya, et al.
(author)
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Disorder-robust phase crystal in high-temperature superconductors stabilized by strong correlations
- 2022
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In: npj Quantum Materials. - : Springer Science and Business Media LLC. - 2397-4648. ; 7:1
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Journal article (peer-reviewed)abstract
- The simultaneous interplay of strong electron–electron correlations, topological zero-energy states, and disorder is yet an unexplored territory but of immense interest due to their inevitable presence in many materials. Copper oxide high-temperature superconductors (cuprates) with pair breaking edges host a flat band of topological zero-energy states, making them an ideal playground where strong correlations, topology, and disorder are strongly intertwined. Here we show that this interplay in cuprates generates a fully gapped ‘phase crystal’ state that breaks both translational and time-reversal invariance, characterized by a modulation of the d-wave superconducting phase co-existing with a modulating extended s-wave superconducting order. In contrast to conventional wisdom, we find that this phase crystal state is remarkably robust to omnipresent disorder, but only in the presence of strong correlations, thus giving a clear route to its experimental realization.
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| 3. |
- Chakraborty, Debmalya, et al.
(author)
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Interplay of finite-energy and finite-momentum superconducting pairing
- 2022
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:2
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Journal article (peer-reviewed)abstract
- Understanding the nature of Cooper pairs is essential to describe the properties of superconductors. The original proposal of Bardeen, Cooper, and Schrieffer (BCS) was based on electrons pairing with same energy and zero center-of-mass momentum. With the advent of new superconductors, different forms of pairing have been discussed. In particular, Cooper pairs with finite center-of-mass momentum have received large interest. Along with such finite-momentum pairs, pairing of electrons at different energies is also central to understanding some superconductors. Here, we investigate the interplay of finite-momentum and finite-energy Cooper pairs considering two different systems: a conventional s-wave superconductor under applied magnetic field and a d-wave finite-momentum pairing state in the absence of magnetic field relevant to correlated superconductors. Investigating both these systems, we find finite-energy pairs persisting independently of finite-momentum pairing, and that they lead to odd-frequency superconducting correlations. We contrast this finding by showing that the even-frequency correlations are predominantly driven by zero-energy pairs for most frequencies. We further calculate the Meissner effect and find that odd-frequency correlations are essential for correctly describing the Meissner effect.
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| 4. |
- Chakraborty, Debmalya, et al.
(author)
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Odd-frequency pair density wave correlations in underdoped cuprates
- 2021
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In: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 23:3
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Journal article (peer-reviewed)abstract
- Pair density waves, identified by Cooper pairs with finite center-of-mass momentum, have recently been observed in copper oxide based high T-c superconductors (cuprates). A charge density modulation or wave is also ubiquitously found in underdoped cuprates. Within a general mean-field one-band model we show that the coexistence of charge density waves (CDWs) and uniform superconductivity in d-wave superconductors like cuprates, generates an odd-frequency spin-singlet pair density wave, in addition to the even-frequency counterparts. The strength of the induced odd-frequency pair density wave depends on the modulation wave vector of the CDW, with the odd-frequency pair density waves even becoming comparable to the even-frequency ones in parts of the Brillouin zone. We show that a change in the modulation wave vector of the CDW from bi-axial to uni-axial, can enhance the odd-frequency component of the pair density waves. Such a coexistence of superconductivity and uni-axial CDW has already been experimentally verified at high magnetic fields in underdoped cuprates. We further discuss the possibility of an odd-frequency spin-triplet pair density wave generated in the coexistence regime of superconductivity and spin density waves, applicable to the iron-based superconductors. Our work thus presents a route to bulk odd-frequency superconductivity in high T-c superconductors.
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| 5. |
- Chakraborty, Debmalya, et al.
(author)
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Quasiparticle Interference as a Direct Experimental Probe of Bulk Odd-Frequency Superconducting Pairing
- 2022
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 129:24
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Journal article (peer-reviewed)abstract
- We show that quasiparticle interference (QPI) due to omnipresent weak impurities and probed by Fourier transform scanning tunneling microscopy and spectroscopy acts as a direct experimental probe of bulk odd -frequency superconducting pairing. Taking the example of a conventional s-wave superconductor under applied magnetic field, we show that the nature of the QPI peaks can only be characterized by including the odd-frequency pairing correlations generated in this system. In particular, we identify that the defining feature of odd-frequency pairing gives rise to a bias asymmetry in the QPI, present generically in materials with odd-frequency pairing irrespective of its origin.
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| 6. |
- Chakraborty, Debmalya, et al.
(author)
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Zero-field finite-momentum and field-induced superconductivity in altermagnets
- 2024
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 110:6
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Journal article (peer-reviewed)abstract
- We explore the possibilities for spin-singlet superconductivity in newly discovered altermagnets. Investigating d-wave altermagnets, we show that finite-momentum superconductivity can easily emerge in altermagnets even though they have no net magnetization, when the superconducting order parameter also has d-wave symmetry with nodes coinciding with the altermagnet nodes. Additionally, we find a rich phase diagram when both altermagnetism and an external magnetic field are considered, including superconductivity appearing at high magnetic fields from a parent zero-field normal state.
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| 7. |
- Wu, Xianxin, et al.
(author)
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Crossover between electron-electron and electron-phonon mediated pairing on the kagome lattice
- 2024
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:1
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Journal article (peer-reviewed)abstract
- We study electron-electron and electron-phonon mediated pairing in the Holstein extended Hubbard model on the kagome lattice near the van Hove fillings, and we investigate their combined effects on electron pairing states. We find that their combination can promote exotic pairings in a crossover region, where the filling is close to a van Hove singularity. In particular, at the p-type van Hove filling, the E1u (p-wave) and B2u(fy3-3yx2-wave) pairings become leading, and at the m-type van Hove filling, the E1u and A2g (i-wave) pairings get promoted. Moreover, we show that the electron-phonon interaction acquires a significant momentum dependence, due to the sublattice texture of the Fermi surfaces, which can promote non-s-wave pairing. We present a detailed analysis of these pairing propensities, and we discuss implications for the vanadium-based kagome superconductors AV3Sb5.
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