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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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Representative ZF and wTF μSR data.(a) ZF μSR time-spectra of CrAs measured at T = 5 K and p = 1 bar. The solid line is a fit according to the theoretical field distribution caused by incommensurate helimagnetic order shown in the inset [see the Supplemental materials for details]. The minimum (Bmin) and the maximum (Bmax) cutoff fields are represented by vertical dashed lines. (b) and (c) depict the temperature evolution of the non-magnetic volume fraction f of CrAs obtained in the wTF μSR measurements at p = 2.5 and 5.55 kbar, respectively. Closed and open symbols correspond to the experimental data obtained with increasing and decreasing temperature (the sweeping rate is  K/min, 5 minutes per data point). The clear hysteresis is indicative of a first order magnetic transition.
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f1: Representative ZF and wTF μSR data.(a) ZF μSR time-spectra of CrAs measured at T = 5 K and p = 1 bar. The solid line is a fit according to the theoretical field distribution caused by incommensurate helimagnetic order shown in the inset [see the Supplemental materials for details]. The minimum (Bmin) and the maximum (Bmax) cutoff fields are represented by vertical dashed lines. (b) and (c) depict the temperature evolution of the non-magnetic volume fraction f of CrAs obtained in the wTF μSR measurements at p = 2.5 and 5.55 kbar, respectively. Closed and open symbols correspond to the experimental data obtained with increasing and decreasing temperature (the sweeping rate is  K/min, 5 minutes per data point). The clear hysteresis is indicative of a first order magnetic transition.

Mentions: In the low-pressure region,  kbar, spontaneous muon spin precession is clearly seen in the ZF μSR time spectra (see Fig. 1a) thus confirming that long range magnetic order is established below TN. The oscillating part of the signal is accurately described by a field distribution characterized by a minimum (Bmin) and a maximum (Bmax) cutoff field (see the inset in Fig. 1a), which is consistent with the observation of helimagnetic incommensurate magnetic order45678. The relatively high values of the cutoff fields ( T and T at p = 1 bar) are in agreement with the large moments as obtained by means of neutron powder diffraction4. The wTF μSR experiments performed at ambient pressure and at p = 2.5 kbar show relatively sharp transitions to the magnetic state and prove that the magnetism occupies close to 100% of the sample volume (see Fig. 1b and Fig. Sup 3 in the Supplemental material). The hysteresis in TN signifies a first order magnetic phase transition.


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)

Representative ZF and wTF μSR data.(a) ZF μSR time-spectra of CrAs measured at T = 5 K and p = 1 bar. The solid line is a fit according to the theoretical field distribution caused by incommensurate helimagnetic order shown in the inset [see the Supplemental materials for details]. The minimum (Bmin) and the maximum (Bmax) cutoff fields are represented by vertical dashed lines. (b) and (c) depict the temperature evolution of the non-magnetic volume fraction f of CrAs obtained in the wTF μSR measurements at p = 2.5 and 5.55 kbar, respectively. Closed and open symbols correspond to the experimental data obtained with increasing and decreasing temperature (the sweeping rate is  K/min, 5 minutes per data point). The clear hysteresis is indicative of a first order magnetic transition.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Representative ZF and wTF μSR data.(a) ZF μSR time-spectra of CrAs measured at T = 5 K and p = 1 bar. The solid line is a fit according to the theoretical field distribution caused by incommensurate helimagnetic order shown in the inset [see the Supplemental materials for details]. The minimum (Bmin) and the maximum (Bmax) cutoff fields are represented by vertical dashed lines. (b) and (c) depict the temperature evolution of the non-magnetic volume fraction f of CrAs obtained in the wTF μSR measurements at p = 2.5 and 5.55 kbar, respectively. Closed and open symbols correspond to the experimental data obtained with increasing and decreasing temperature (the sweeping rate is  K/min, 5 minutes per data point). The clear hysteresis is indicative of a first order magnetic transition.
Mentions: In the low-pressure region,  kbar, spontaneous muon spin precession is clearly seen in the ZF μSR time spectra (see Fig. 1a) thus confirming that long range magnetic order is established below TN. The oscillating part of the signal is accurately described by a field distribution characterized by a minimum (Bmin) and a maximum (Bmax) cutoff field (see the inset in Fig. 1a), which is consistent with the observation of helimagnetic incommensurate magnetic order45678. The relatively high values of the cutoff fields ( T and T at p = 1 bar) are in agreement with the large moments as obtained by means of neutron powder diffraction4. The wTF μSR experiments performed at ambient pressure and at p = 2.5 kbar show relatively sharp transitions to the magnetic state and prove that the magnetism occupies close to 100% of the sample volume (see Fig. 1b and Fig. Sup 3 in the Supplemental material). The hysteresis in TN signifies a first order magnetic phase transition.

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