October 3rd, 2022: Giulia Venditti

On Monday, October 3rd, 2022 from 11 am to 12 am we will host a seminar by Giulia Venditti from CNR-SPIN, Rome.

Title

Filamentary Superconductivity in Systems with Competing Charge Density Wave

Abstract

Filamentary superconductivity is naturally emerging as a new rich field. The higly inhomogeneous nature of the superconducting (SC) condensate has been in fact reported in several families of low dimensional superconductors. The mechanisms behind the fragmentation of the electronic condensate can be several, depending on the specific material and conditions, leading to unusual trends in transport measurements [1] and covering the hallmarks of a Berezinskii-Kosterlitz-Thouless (BKT) transition.

In some class of materials, experimental observations points towards the direction of a phase competition among superconductivity and the charge ordered phase, tunable through an external control parameter, which can be either magnetic field, pressure or doping. Specifically, in TMDs, the SC filaments has been directly observed via scanning tunneling microscopy (STM) measurements [2]; in cuprates, magnetoresistance experiments on LSCO thin films [3, 4], spin susceptibilities [5] and specific heat [6] in YBCO all evidence a fragile SC state surviving at low temperatures in the charge density wave (CDW) state of the phase diagram.

In this work [7, 8], we studied the CDW-SC competition by means of Monte Carlo simulations. We use an anisotropic Heisenberg model on a two-dimensional square lattice that captures the basic symmetries of the problem: the out-of-plane component of the pseudospin sz encodes two possible charge ordered variants (up/down) and the in-plane component stands for the SC order parameter. We construct a phase diagram where the anisotropy term α introduced plays the same role as the magnetic field in real experiments and it can tune the transition from the topological BKT to the CDW (see Fig. 1). Importantly, we find the presence of impurities is necessary in order to stabilize the clustering of polycrystalline charge ordered domains and the appearance of filamentary superconductivity.

Fig. 1: Snapshots of the final configurations of spin at T=0.001 for L=128 varying the control parameter α. The color maps the out-of-plane component from up (sz=+1 in green), to in-plane (sz=0 in red), to down (sz=-1 in blue).

References

[1] G. Venditti et al. Superfluid rigidity in filamentary superconductors, In preparation.

[2] M. Spera et al. Phys. Rev. B 99, 155133 (2019).

[3] B. Leridon et al. New J. Phys. 22 073025 (2020).

[4] S. Caprara et al. SciPost Phys. 8, 003 (2020).

[5] R. Zhou et al. PNAS 1711445114 (2017).

[6] J. Kačmarčík et al. Phys. Rev. Lett. 121, 167002 (2018).

[7] G. Venditti et al. Competition between charge order and superconductivity in 2d systems, In preparation.

[8] G. Venditti et al. Filamentary superconductivity arising from the CDW-SC competition, In preparation.