1. Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strae 40, D-01187 Dresden, Germany
2. Center for Materials Theory, Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855, USA
3. Department of Physics and Astronomy, Rice University, Houston, Texas 77005-1892, USA

Correspondence to: S. Paschen¹ =Email: paschen@cpfs.mpg.de

Abstract

A quantum critical point (QCP) develops in a material at absolute zero when a new form of order smoothly emerges in its ground state. QCPs are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet^{1, 2, 3}. An important unsolved question is whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin-density-wave (SDW) type^{4, 5}, or suddenly, as expected if the heavy electrons are abruptly localized by magnetism^{6, 7, 8}. Here we report measurements of the low-temperature Hall coefficient (R_H)—a measure of the Fermi surface volume—in the heavy-fermion metal YbRh₂Si₂ upon field-tuning it from an antiferromagnetic to a paramagnetic state. R_H undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP.

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