Anisotropic field-induced changes in the superconducting order parameter of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>UT</mml:mi> <mml:msub> <mml:mi mathvariant="normal">e</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math>

Abstract

<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>UT</a:mi> <a:msub> <a:mi mathvariant="normal">e</a:mi> <a:mn>2</a:mn> </a:msub> </a:mrow> </a:math> is a newly discovered unconventional superconductor, where electron Cooper pairs combine into a spin-triplet ground state. We study the specific heat <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>C</c:mi> </c:mrow> </c:math> () of a high-quality <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mi>UT</d:mi> <d:msub> <d:mi mathvariant="normal">e</d:mi> <d:mn>2</d:mn> </d:msub> </d:mrow> </d:math> single crystal, with a single anomaly at a high superconducting transition temperature <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:msub> <f:mi>T</f:mi> <f:mi>c</f:mi> </f:msub> <f:mo>=</f:mo> <f:mn>2.1</f:mn> </f:mrow> </f:math> K and a low residual Sommerfeld coefficient <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi>γ</g:mi> <g:mn>0</g:mn> </g:msub> </g:math> . Applying magnetic fields up to 12 T along the crystallographic axes <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mi>a</h:mi> <h:mo>,</h:mo> <h:mo> </h:mo> <h:mi>b</h:mi> </h:math> , and <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mi>c</i:mi> </i:math> , we observe highly anisotropic behavior in <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:mrow> <j:msub> <j:mi>γ</j:mi> <j:mn>0</j:mn> </j:msub> <j:mrow> <j:mo>(</j:mo> <j:mi>H</j:mi> <j:mo>)</j:mo> </j:mrow> </j:mrow> </j:math> . Below 4 T, <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:mrow> <k:msub> <k:mi>γ</k:mi> <k:mn>0</k:mn> </k:msub> <k:mrow> <k:mo>(</k:mo> <k:mi>H</k:mi> <k:mo>)</k:mo> </k:mrow> <k:mo>≈</k:mo> <k:mi>γ</k:mi> <k:mn>0</k:mn> <k:mo>+</k:mo> <k:mi>λ</k:mi> <k:mi>i</k:mi> <k:mi>√</k:mi> <k:mi>H</k:mi> </k:mrow> </k:math> ( <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:mrow> <l:mi>i</l:mi> <l:mo>=</l:mo> <l:mi>a</l:mi> <l:mo>,</l:mo> <l:mi>b</l:mi> <l:mo>,</l:mo> <l:mi>c</l:mi> </l:mrow> </l:math> ), which is expected for an unconventional superconductor with nodes on the Fermi surface away from the direction of the magnetic field. At 4 T ( <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mi>a</m:mi> </m:math> and <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"> <n:mi>b</n:mi> </n:math> axes) and 5.5 T ( <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"> <o:mi>c</o:mi> </o:math> axis), distinctive changes in the behavior of <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:mrow> <p:msub> <p:mi>γ</p:mi> <p:mn>0</p:mn> </p:msub> <p:mrow> <p:mo>(</p:mo> <p:mi>H</p:mi> <p:mo>)</p:mo> </p:mrow> </p:mrow> </p:math> suggest that a stable low-field ground state begins to evolve above 4 T. The data analysis indicates that the nodes are located near the <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"> <q:mrow> <q:mi>a</q:mi> <q:mo>–</q:mo> <q:mi>b</q:mi> </q:mrow> </q:math> plane, with possible order parameters <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"> <r:mrow> <r:msub> <r:mi>d</r:mi> <r:mrow> <r:mi mathvariant="normal">B</r:mi> <r:mn>2</r:mn> <r:mi mathvariant="normal">u</r:mi> </r:mrow> </r:msub> <r:mo>+</r:mo> <r:mi>i</r:mi> <r:mi>ɛ</r:mi> <r:msub> <r:mi>d</r:mi> <r:mrow> <r:mi mathvariant="normal">B</r:mi> <r:mn>1</r:mn> <r:mi mathvariant="normal">u</r:mi> </r:mrow> </r:msub> </r:mrow> </r:math> or <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"> <w:mrow> <w:msub> <w:mi>d</w:mi> <w:mrow> <w:mi mathvariant="normal">B</w:mi> <w:mn>2</w:mn> <w:mi mathvariant="normal">u</w:mi> </w:mrow> </w:msub> <w:mo>+</w:mo> <w:mi>i</w:mi> <w:mi>ɛ</w:mi> <w:msub> <w:mi>d</w:mi> <w:mi>Au</w:mi> </w:msub> </w:mrow> </w:math> . Our findings support <z:math xmlns:z="http://www.w3.org/1998/Math/MathML"> <z:msub> <z:mi>B</z:mi> <z:mrow> <z:mn>2</z:mn> <z:mi mathvariant="normal">u</z:mi> </z:mrow> </z:msub> </z:math> as the primary superconducting order parameter in <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML"> <bb:mrow> <bb:mi>UT</bb:mi> <bb:msub> <bb:mi mathvariant="normal">e</bb:mi> <bb:mn>2</bb:mn> </bb:msub> </bb:mrow> </bb:math> .

Topics & Concepts