Pressure-induced magnetic quantum critical point and unconventional

Transcription

1 Institute of Physics, CAS Pressure-induced magnetic quantum critical point and unconventional superconductivity in CrAs and MnP Jinguang Cheng SchoolandWorkshoponStronglyCorrelatedElectronicSystems- NovelMaterialsandNovelTheories ICTPTrieste

2 Collaborators J. L. Luo, W. Wu, J. P. Sun, C. Q. Jin, P. J. Sun, N. L. Wang Y. Uwatoko, K. Matsubayashi M. Matsuda, J. Q. Yan Q. Si Q R. Yu

3 OUTLINE 1 QCP and unconventional SC 2 P-induced SC in CrAs 3 P-induced SC in MnP 4 Conclusion and outlooks

4 Quantum critical point (QCP) * / T m /m T N Ordered phase SC Coleman & Schofield, Nature (25) Si & Steglich, Science (21) Sachdev & Keimer, Phys. Today (211) c QCP Fermi liquid (x, P, H, etc) Non Fermi liquid T n (1 n < 2) C e /T lnt

5 QCP and unconventional SC Chem mical dopin ng Pressure Advantages clean fine and precise

6 SC Cr- and Mn-based superconductor?

7 OUTLINE 1 QCP and unconventional SC 2 P-induced SC in CrAs 3 P-induced SC in MnP 4 Conclusion and outlooks

8 1 st order AF transition of CrAs Orthorhombic MnPtype crystal structure Helimagnetic structure 1.7μ B /Cr Pnma (62) a = Å b = Å c = Å Q = c* 1,2 = 3,4 = 12 2,3 = 4,1 = ~4% Acta. Chem. Scan. 25, 173 (1971); JPSJ 3, 1319 (1971) T N = 265 K

9 Earlier high pressure studies and motivation T N AF Sov. Phys. JETP 51, 542 (198)? What will happen at the magnetic critical point? Superconductivity??

10 High-quality CrAs single crystals are important 1mm a

11 HP measurements on the CrAs crystals Resistivity Ac magnetic susceptibility Piston cylinder cell Pressure manometer: Pb P(kbar) = (7.2 T c )/.365 Pressure medium: Glycerol Pb CrAs Pb+CrAs

12 Discovery of P-induced SC in CrAs ( cm) bar 1.73 kbar #6 RRR =24 (a) 3 ( cm m) cm) ( bar (b) (c) 2.

13 Bulk SC evidenced from ac susceptibility kbar

14 T-P phase diagram of CrAs 4 T=.4 4K AF #6, #7, #9, T N cool from #9, T N warm from T N warm from dc- T N #6, #7, #9, T c from 1 AF+SC #6, T c from ac- #7a, T c from in PCAC 2 T c Bulk SC Pressure (kbar) RRR #6 24 (a) #7 327 # (b) T c (K)

15 A 2 Cr 3 As 3 (A=K, Rb, Cs) (G. Cao, Zhejiang Univ.) PRX (215) PRB (215) SCM(215) Kotegawa, JPSJ (214), PRL (215)

16 SC sensitive to disorder #3 RRR = 45 ( cm) #3 RRR = kbar bar 12 ( cm) P / kbar bar T N 5 T c 3 #3 # P (Kbar) 8 1

17 Coherent length vs Mean free path H c2 (T) P = 9. 5 kbar L mfp = R H m 3 /C at 5 K n = m 3 mfp.2.. H c2 () =.96(2) T T c () = 1.56(5) K = 1.41(6).4.8 T c (K) 1.2 μ H c2 (T) = μ H c2 () {1 [T c /T c ()] α } μ H c2 () = /2 2 = 185 Å 1.6 RRR ~25 = m L mfp = 766 Å mfp RRR ~5 8 = m L mfp = 153 Å

18 Neutron scattering: Phys. vs Chem. P Physical pressure b (Å) Chemical 3.5 pressure 3.45 Structuret Magnetic order (a) kbar 9 kbar 3.5 kbar 1 bar x =. x =.35 x =.5 12 kbar (c) CrAs 1 x P x

19 Inelastic neutron scattering CrAs 3K P6% 5K CrAs 1K NNN AFM correlations

20 Evidence for quantum criticality: Enhanced m* ( cm m) P (kbar) T 2 (K 2 ) 8 (a) Piston cylid der cell Palm Cubi ic cell ( cm) ) A (1-9 cm P c 2 4 P (Kbar) Enhancement of A coefficient near P c ; A (m*/m ) 2 (b) (c) 6

21 ( cm) Evidence for quantum criticality: nfl P (kbar) Palm cubi ic cell Piston cylind der cell n 2. = +BT n #9 1 P c P (kbar) 5 #6 #7 6 7

22 Further evidences for quantum criticality T (K ) ( cm) CrAs 1-x P x x =. x =.3 x =.4 x = x = ( cm) (f) CrAs 1-x P x T 2 (K 2 ) A (1-9 cmk -2 ) x )4 C/T (mj/m molk x c 2 ( ).1 A (h).5.15 (g).1.2 x CrAs 1-x P x. 2 4 T 2 (K 2 ) (mj/m mol K 2 ) x in CrAs 1-x P x

23 Mn-based superconductor? Nat. Comm. 5, 558 (214) SC Mn-based superconductor?

24 Strategy Magnetic moment vs. b axis length MnAs MnSb CrSb M X 2.5 M ( B ) MnAs.88 P.12 MnP CrAs a.5 CrP. 3. CrAs.9 P b (Å) MnP would be the a good start point to approach a magnetic instability by the application of high pressure!!! 4. c b Hexagonal lnia NiAs (solid line) Orthorhombic MnP (dash lines)

25 Physical properties of MnP at ambient pressure H // b ) M( B /Mn H (T T) 5 4 H b 3 2 Fan PM ( cm) I b 1 T s 1 I // b 2 T c 3 Screw FM //b 5 T s 5 K T c = K

26 Earlier high-pressure studies J. Solid State Chem. 4, 391 (1972) 3 5kbar: Solid PTM

27 HP techniques with extended pressure capacity Cubic anvil cell Opposed-Anvil Cell Pmax : 15 GPa P-medium : Glycerol Cheng JG, RSI (214) Pmax : 12 GPa P-medium : Ar Kitagawa, JPSJ (21)

28 d / /dt (a.u.) cm) ( # Cubic anvil cell (b) (a) 2.8 GPa GPa 3 ( cm) ( cm) # GPa #2 # P suppresses the magnetic transition; Possible SC appears near the magnetic instability; P may alter the nature of magnetic transition GPa

29 HP: Opposite anvil cell GPa (a) # 3 #3 ( c m) # GPa Pb #4 Nearly perfect diamagnetic signal confirms the P induced SC with a T SC 1K in MnP; (b) SC exists within a narrow pressure range where the magnetic transition just vanishes;

30 T-P phase diagram of MnP 5 3 c ( cm) TC PM FM T* TS ' ((a.u.) 2 T GPa s AFM? 2 TSC P (GPa) T* 1.5 GPa GPa GPa GPa GPa.91 GPa GPa GPa SC

31 Signatures of AFM QCP ( cm) 2 2. ( cm) GPa 4 8 T 1.5 (K 1.5 ) (a) GPa T 2 (K 2 ) A (1-9 cm) ( cm) (b) (c) 2 P c 4 6 P (GPa) 8 1 non Fermi liquid behavior and dramatic enhancement of effective mass m* near P c Cheng et al. PRL (215)

32 Conclusion and outlooks P induced magnetic QCP is an important approach to search for unconventional SC, e.g. CrAs and MnP. Expected to have more Cr and Mn based SCs. Open questions: What is the specialty for the helimagnetic QCP? Can we also realized SC in other helimagnets: FeP, FeAs? Nature of the AFM order in MnP?