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Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs.

Khasanov R, Guguchia Z, Eremin I, Luetkens H, Amato A, Biswas PK, Rüegg C, Susner MA, Sefat AS, Zhigadlo ND, Morenzoni E - Sci Rep (2015)

Bottom Line: The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar.At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure.Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs).

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.

ABSTRACT
The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 < or ~  p < or ~ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.

No MeSH data available.


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Temperature-pressure phase diagram.(a) Pressure dependence of the non-magnetic volume fraction f; (b) maximum cutoff field Bmax, which is proportional to the ordered moment ; (c) superconducting transition temperature Tc; and (d) the zero-temperature value of the inverse squared magnetic penetration depth . The grey area represents the pressure region where magnetism and superconductivity coexist. The solid line in (b) is a linear fit with  (see the Supplemental materials).
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f3: Temperature-pressure phase diagram.(a) Pressure dependence of the non-magnetic volume fraction f; (b) maximum cutoff field Bmax, which is proportional to the ordered moment ; (c) superconducting transition temperature Tc; and (d) the zero-temperature value of the inverse squared magnetic penetration depth . The grey area represents the pressure region where magnetism and superconductivity coexist. The solid line in (b) is a linear fit with (see the Supplemental materials).

Mentions: The measured λ−2(T) and the internal field B(T) of CrAs for p = 4.06, 4.9, 5.8, 6.7, 8.6 and 10.3 kbar are shown in Fig. 2a,b. Note that λ−2 and B were derived from the fraction of the sample remaining in the non-magnetic state down to the lowest temperature (see Fig. 3a). Due to the strongly damped signal in the magnetic phase one is unable to measure any superconducting response in the magnetic fraction of the sample. We believe, however that superconductivity in CrAs cannot emerge in the magnetically ordered parts for two following reasons. First, Wu et al.1 have shown that the low-temperature diamagnetic susceptibility (χdia) of CrAs is nearly zero for pressures  kbar, increases linearly in the range and reaches its maximum value, close to the ideal χdia = −1/4π, for pressures exceeding 7.85 kbar. It follows almost exactly the pressure dependence of the non-magnetic fraction f as observed in our wTF and TF μSR experiments (see Fig. 3a). Second, the large magnetic moment and its weak reduction as a function of pressure (see Fig. 3b) require the separation of CrAs in superconducting and magnetic domains. This is e.g. the case for the so-called ‘245’ family of Fe-based superconductors1516, which is characterized by the high value of both, magnetic moment (~3μB) and Néel temperature (TN ~ 500 K)17181920. Note that within the full pressure range studied here the value of the ordered magnetic moment in CrAs is only a factor of two smaller than that in ‘245’ superconductors.


Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs.

Khasanov R, Guguchia Z, Eremin I, Luetkens H, Amato A, Biswas PK, Rüegg C, Susner MA, Sefat AS, Zhigadlo ND, Morenzoni E - Sci Rep (2015)

Temperature-pressure phase diagram.(a) Pressure dependence of the non-magnetic volume fraction f; (b) maximum cutoff field Bmax, which is proportional to the ordered moment ; (c) superconducting transition temperature Tc; and (d) the zero-temperature value of the inverse squared magnetic penetration depth . The grey area represents the pressure region where magnetism and superconductivity coexist. The solid line in (b) is a linear fit with  (see the Supplemental materials).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561900&req=5

f3: Temperature-pressure phase diagram.(a) Pressure dependence of the non-magnetic volume fraction f; (b) maximum cutoff field Bmax, which is proportional to the ordered moment ; (c) superconducting transition temperature Tc; and (d) the zero-temperature value of the inverse squared magnetic penetration depth . The grey area represents the pressure region where magnetism and superconductivity coexist. The solid line in (b) is a linear fit with (see the Supplemental materials).
Mentions: The measured λ−2(T) and the internal field B(T) of CrAs for p = 4.06, 4.9, 5.8, 6.7, 8.6 and 10.3 kbar are shown in Fig. 2a,b. Note that λ−2 and B were derived from the fraction of the sample remaining in the non-magnetic state down to the lowest temperature (see Fig. 3a). Due to the strongly damped signal in the magnetic phase one is unable to measure any superconducting response in the magnetic fraction of the sample. We believe, however that superconductivity in CrAs cannot emerge in the magnetically ordered parts for two following reasons. First, Wu et al.1 have shown that the low-temperature diamagnetic susceptibility (χdia) of CrAs is nearly zero for pressures  kbar, increases linearly in the range and reaches its maximum value, close to the ideal χdia = −1/4π, for pressures exceeding 7.85 kbar. It follows almost exactly the pressure dependence of the non-magnetic fraction f as observed in our wTF and TF μSR experiments (see Fig. 3a). Second, the large magnetic moment and its weak reduction as a function of pressure (see Fig. 3b) require the separation of CrAs in superconducting and magnetic domains. This is e.g. the case for the so-called ‘245’ family of Fe-based superconductors1516, which is characterized by the high value of both, magnetic moment (~3μB) and Néel temperature (TN ~ 500 K)17181920. Note that within the full pressure range studied here the value of the ordered magnetic moment in CrAs is only a factor of two smaller than that in ‘245’ superconductors.

Bottom Line: The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar.At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure.Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs).

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.

ABSTRACT
The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 < or ~  p < or ~ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.

No MeSH data available.


Related in: MedlinePlus