Sharp quantum phase transition in the frustrated spin-1/2 Ising chain antiferromagnet CaCoV2O7

We report on a quantum critical behavior in the quasi-1D spin-1/2 zigzag frustrated chain antiferromagnet <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>CaCoV</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>7</a:mn></a:msub></a:mrow></a:math>, induced by an applied magnetic field. Below <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msub><c:mi>T</c:mi><c:mi>N</c:mi></c:msub><c:mo>=</c:mo><c:mn>3.3</c:mn></c:mrow></c:math> K our zero-field neutron diffraction studies revealed the up-up-down-down spin structure, stabilized by an order-by-disorder phenomenon. At base temperature, the magnetic order is suppressed by an applied magnetic field (<d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mi>B</d:mi></d:math>), inducing a transition into a quantum paramagnetic state at <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:msub><e:mi>B</e:mi><e:mi>c</e:mi></e:msub><e:mo>=</e:mo><e:mn>3</e:mn></e:mrow></e:math> T, as revealed by both neutron diffraction and ESR data. The transition exhibits an unusually sharp phase boundary with the critical exponent <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mi>ϕ</f:mi><f:mo>=</f:mo><f:mn>0.164</f:mn><f:mo>(</f:mo><f:mn>3</f:mn><f:mo>)</f:mo><f:mo>≈</f:mo><f:mn>1</f:mn><f:mo>/</f:mo><f:mn>6</f:mn></f:mrow></f:math>, in contrast to the earlier experimental observations for uniform spin-1/2 chain systems. Such a sharp QPT is anticipated due to a rare combination of spin-orbit coupling and competing NN and NNN exchange interactions <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:msub><g:mi>J</g:mi><g:mn>1</g:mn></g:msub></g:math> and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:msub><h:mi>J</h:mi><h:mn>2</h:mn></h:msub></h:math> of the zigzag spin chain.