A mechanism for ‘hidden’ magnetic memory: Recently an intriguing observation of hidden magnetic memory which induces spontaneous vortices in the superconducting state of 4Hb-TaS2 has been reported [Nature, 607, 692, 2022]. Motivated by this observation, we present a mechanism which could lead to such an observation. This mechanism relies on the possibility of spin-charge separation induced by strong electronic correlations, something which is not unexpected in 4Hb-TaS2, and might be applicable for a much broader class of materials. For concreteness we demonstrate the feasibility of this mechanism on a bilayer square lattice where electrons in one of the layers are described by a t-J model (cf 1T layer of the 4Hb system), while the electrons in the other layer are essentially non-interacting (cf 1H layer of the 4Hb system). Within a parton description of the strongly correlated layer we demonstrate the existence of a phase above the superconducting transition temperature of the system which can be trained by an external magnetic field and which produces an immeasurably small magnetic field when the external magnetic field is switched off. In our description this ‘hidden’ magnetic phase is a spinonic superconductor with induced vortices. At the superconducting transition temperature of the system the holons condense into a coherent phase converting the spinonic vortices into superconducting vortices while also inducing superconductivity in the non-interacting layer by proximity effect. This mechanism is capable of capturing some of the essential observations made in the experiments on 4Hb-TaS2 . This work is being done in collaboration with Jonathan Ruhman and Efrat Shimshoni at the Bar-Ilan University, Israel and Debanjan Choudhury at the Cornell University, USA.
Simulating quantum anomalous heat flows using NISQ devices: Understanding the role of genuine quantum features, such as coherence and quantum correlations, in the energy flow has been the focus of recent theoretical and experimental research. Theoretical bounds on the heat flow between two local thermal states with initial quantum correlations have been derived. In turn, it has been proven that the fluctuations of the exchanged heat can be described by means of quasiprobability distributions, whose negativities can reliably identify aspects beyond classical thermodynamics [PRX Qunatum 1, 010309 (2020)]. Quite recently, these non-classical features of thermodynamic quantities have been experimentally probed utilizing NMR and quantum optical platforms. We use state-of-the-art quantum processors to probe the energy exchange between two qubits sharing quantum correlations. We then look for signatures of quantum anomalous energy flow linked to dynamics of the quantum correlated state. This work is being done in collaboration with Loris Maria Cangemi, Amikam Levy and Emanuele Dalla Torre at the Bar-Ilan University, Israel.
On the observed unconventional nature of superfluid stiffness in overdoped cuprates: It was long believed that the nature of superconductivity in the overdoped copper oxide high transition temperature superconductors is conventional. However, measurements of the superfluid stiffness in these superconductors have been at odds with this expectation. In this regard it was proposed that the impurities and/or inhomogeneities intrinsic to these samples could explain the observed deviation from a conventional superconductor. Interestingly, recent measurements on ultra-clean and highly homogeneous samples uphold their unconventional nature and have once again brought this question to the forefront of condensed matter research [see PRB 103, 024528 (2021) and references therein]. Cearly, a theory which can explain the unconventional nature of superfluid stiffness in these materials without invoking the role of impurities or inhomogeneities is desirable. We address this issue at two levels. First, within a Ginzburg-Landau description we show that in the presence of a soft internal phase mode, whose possibility in the context of cuprates has recently been highlighted [EPL 119, 27004, 2017 & PRL 124, 147002, 2020], the Anderson-Higgs mechanism is modified in such a way that the London penetration depth measured in experiments can be much longer than what one expects from conventional wisdom. Second, within a microscopic model appropriate for the cuprates we compute the temperature dependence of the superfluid stiffness to show that they indeed resemble the experimental observations and argue based on our earlier calculations [PRL 124, 147002, 2020] that the fluctuations in the soft internal phase mode when accounted for self-consistently may lead to a quantitative agreement with the experiments.