Pressure-Tuned Quantum Criticality in the Locally Noncentrosymmetric Superconductor CeRh2As2

The unconventional superconductor <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mrow><a:msub><a:mrow><a:mi>CeRh</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msub></a:mrow><a:mrow><a:msub><a:mrow><a:mi>As</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msub></a:mrow></a:mrow></a:math> (critical temperature <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:msub><c:mrow><c:mi>T</c:mi></c:mrow><c:mrow><c:mi mathvariant="normal">c</c:mi></c:mrow></c:msub><c:mo>≈</c:mo><c:mn>0.4</c:mn><c:mtext> </c:mtext><c:mtext> </c:mtext><c:mi mathvariant="normal">K</c:mi></c:mrow></c:math>) displays an exceptionally rare magnetic-field-induced transition between two distinct superconducting (SC) phases, proposed to be states of even and odd parity of the SC order parameter, which are enabled by a locally noncentrosymmetric structure. The superconductivity is preceded by a phase transition of unknown origin at <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:msub><g:mrow><g:mi>T</g:mi></g:mrow><g:mrow><g:mn>0</g:mn></g:mrow></g:msub><g:mo>=</g:mo><g:mn>0.5</g:mn><g:mtext> </g:mtext><g:mtext> </g:mtext><g:mi mathvariant="normal">K</g:mi></g:mrow></g:math>. Electronic low-temperature properties of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mrow><j:msub><j:mrow><j:mi>CeRh</j:mi></j:mrow><j:mrow><j:mn>2</j:mn></j:mrow></j:msub></j:mrow><j:mrow><j:msub><j:mrow><j:mi>As</j:mi></j:mrow><j:mrow><j:mn>2</j:mn></j:mrow></j:msub></j:mrow></j:math> show pronounced non-Fermi-liquid behavior, indicative of a proximity to a quantum critical point (QCP). The role of quantum fluctuations and normal state orders for the superconductivity in a system with staggered Rashba interaction is currently an open question, pertinent to explaining the occurrence of the two-phase superconductivity. In this work, using measurements of resistivity and specific heat under hydrostatic pressure, we show that the <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:msub><l:mi>T</l:mi><l:mn>0</l:mn></l:msub></l:math> order vanishes completely at a modest pressure of <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:msub><n:mi>P</n:mi><n:mn>0</n:mn></n:msub><n:mo>≈</n:mo><n:mn>0.5</n:mn><n:mtext> </n:mtext><n:mtext> </n:mtext><n:mi>GPa</n:mi></n:math>, revealing a QCP. In line with the quantum criticality picture, the linear temperature dependence of the resistivity at <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:msub><p:mi>P</p:mi><p:mn>0</p:mn></p:msub></p:math> evolves into a Fermi-liquid quadratic dependence as quantum critical fluctuations are suppressed by increasing pressure. Furthermore, the domelike behavior of <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:msub><r:mi>T</r:mi><r:mi mathvariant="normal">c</r:mi></r:msub></r:math> around <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:msub><u:mi>P</u:mi><u:mn>0</u:mn></u:msub></u:math> implies that the fluctuations of the <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:msub><w:mi>T</w:mi><w:mn>0</w:mn></w:msub></w:math> order are involved in the SC pairing mechanism. Published by the American Physical Society 2024