Reply to P. Ao's Comment on "Sign reversing Hall effect in atomically thin high temperature superconductors"

TL;DR

This paper refutes P. Ao's claim that vortex many-body effects cause Hall sign reversal in thin high-temperature superconductors, based on experimental evidence contradicting the theoretical predictions.

Contribution

It provides experimental data that challenge the vortex many-body explanation for Hall sign reversal in atomically thin cuprate superconductors.

Findings

Experimental results are incompatible with Ao's vortex effect predictions.

Supports alternative mechanisms for Hall sign reversal.

Clarifies the limitations of vortex many-body theories in this context.

Abstract

We respond to P. Ao's comment in arXiv:1907.09263, which suggests that vortex many-body effects are the origin of Hall sign reversal in few-unit-cell thick Bi-2212 cuprate crystals (Phys. Rev. Lett. 122, 247001 (2019)). Our experimental results are incompatible with the theoretical predictions detailed in Ao's comment.

Full text

Reply to P. Ao’s Comment on ”Sign reversing Hall effect in atomically thin high temperature superconductors”

S. Y. Frank Zhao

Department of Physics, Harvard University, Cambridge, MA 02138, USA

  

Nicola Poccia

Department of Physics, Harvard University, Cambridge, MA 02138, USA

  

Margaret G. Panetta

Department of Physics, Harvard University, Cambridge, MA 02138, USA

  

Cyndia Yu

Department of Physics, Harvard University, Cambridge, MA 02138, USA

  

Jedediah W. Johnson

Department of Physics, Harvard University, Cambridge, MA 02138, USA

  

Hyobin Yoo

Department of Physics, Harvard University, Cambridge, MA 02138, USA

  

Ruidan Zhong

Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA

  

G. D. Gu

Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA

  

Kenji Watanabe

National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan

  

Takashi Taniguchi

National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan

  

Svetlana V. Postolova

Institute for Physics of Microstructures RAS, Nizhny Novgorod 603950,Russia

Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk 630090, Russia

  

Valerii M. Vinokur

Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA

Consortium for Advanced Science and Engineering, Office of Research and National Laboratories, University of Chicago, Chicago, IL 60637, USA

  

Philip Kim

Department of Physics, Harvard University, Cambridge, MA 02138, USA

The essence of Ao’s theory, as he puts it in AoJPCM is that “…the Hall anomaly can be understood based on the vortex vacancy motion in a pinned vortex lattice.” However, the temperature interval where we observe the sign reversal falls mostly into the vortex-liquid regime where vortex lattice, let alone vortex vacancies, do not exist. In simple words, Ao’s theory is not related to the reality of the physical world.

The inability of Ao’s theory to address the experiment can be illustrated comparing two specific predictions made in Ao’s comment to our observations:

According to AoC ; AoJPCM ; AoJS , a “lower critical field” should emerge, below which the Hall sign reversal should vanish. However, as seen in Figure 2a in our paper OurPaper which we re-plot here in Fig1, specifically for low magnetic fields, the Hall resistance is negative (i.e. reverses in sign) at all nonzero magnetic fields, without any hint to the existence of the lower critical field. Neither was lower critical field reported in previous experiments. 2. 2.

Likewise, our data do not support the second prediction of AoC that the Hall conductivity follows an ”Arrhenius law” with an activation energy corresponding to energy for the generation of ”vortex vacancies in the vortex lattice” AoJPCM ; AoC . As seen in Figure 1 Inset, the Hall conductivity does not evolve monotonically with temperature, much less follows an Arrhenius law. In the Supplementary of OurPaper , we show that the Hall sign reversal disappears in our samples below the BKT transition around 60 K. Thus sign reversal indeed exists only in the vortex liquid regime where vortex lattice and, therefore, vortex vacancies simply do not exist. Our data are in full agreement with the findings of all other experiments where the sign reversed Hall effect has been mostly seen in the vortex liquid regime, and where the Hall signal vanishes as the vortex liquid freezes into a solid.

A detailed look at references in Ao’s Comment AoC refutes his claim that his theory was supported by data from various laboratories. Of the 13 papers Ao referenced (Refs. 6-18) in AoC , only one (Ref.[11]) quantitatively compared Ao’s findings to experiment and stated that the observed experimental behavior of Hall conductance deviates from predictions specific to his theory. Reference [8] indicated that Ao’s theory is inapplicable to their experiment, and Refs. [9, 10, 12, 13, 15-18], simply mentioned Ao’s work in passing as one of many citations but did not present any data to support Ao’s theory. Only Ref. [14] claimed in a single sentence that Ao’s theory explains their experiment but did not make any quantitative comparison. And, finally, Ref. [6], which according to Ao ”explicitly tested against data published in PRL” AoC , is Ao’s one-page Comment not presenting a single equation or fit to the experiment.