Interference between s -wave superconductor and Sr 2 RuO 4 Y. Maeno, - PowerPoint PPT Presentation

Novel Quantum Phenomena in Superconducting Sr 2 RuO 4 Interference between s -wave superconductor and Sr 2 RuO 4 Y. Maeno, R. Nakagawa, T. Nakamura, T. Yamagishi, S. Yonezawa, T. Terashima Kyoto University

The “Superclean” Project (FY2005-2009) A04: Anisotropic Superconductors and Superfluids 3 He-A, B Sr 2 RuO 4 (1.5 K) Sr 2 RuO 4 -Ru (3 K) 3 He-A-like A04g : Maeno (Kyoto) A04h : Ishikawa (Osaka City) BULK Ishida EUTECTICS Kashiwaya 共晶 Yonezawa Kambara M a e n o INTERFACES Miyake Tanaka

Posters on Ruthenate SupeC P121 Kittaka: T c of pure Sr 2 RuO 4 can be as high as 3.2 K ! P123 Nakagawa: Pb/Ru/Sr 2 RuO 4 proximity junctions P 116 Karaki, P118 Tenya: Magnetization curves P119 Ishida: NMR review P139 Kashiwaya: Microdevices P117 Nomura, P120 H.Ikeda, P124 Yanase: d -vector orientation (theories) P138 Sakaki: E -induced M-I transition in Ca 2 RuO 4

Novel Quantum Phenomena in Superconducting Sr 2 RuO 4 Interference between s -wave superconductor and Sr 2 RuO 4 Y. Maeno, R. Nakagawa, T. Nakamura, T. Yamagishi, S. Yonezawa, T. Terashima Kyoto University

Pairing Symmetry of Sr 2 RuO 4 →？ Spins : S = 1, S z = 0 orbital Spin moment ・ NMR Knight shifts ・ Polarized neutrons ➜ Spin Triplet Pairing Orbital moment: L = 1, L z = 1 spins Broken T Orbital ・  SR ・ Vortex lattice ・ Kerr effect d = z  0 ( k x + ik y ) ➜ Broken Time Reversal Symmetry A.P. Mackenzie and Y. Maeno, ・ Josephson effect ・ chiral domains ➜ Odd Parity ( p -wave) Rev. Mod. Phys. 75 , 657 (2003).

Spin Orientation ( d d - -vector vector) in Sr 2 RuO 4 Orbital Yoshioka & Miyake, Both spin states are L z =+1 Agterberg compatible with NMR experiments. Murakawa, Ishida et al. Spins ⇒ d // z d // x S z =0 Half-quantum vortex (HQV) is possible, with the rotation of the d -vector (spin) by π , and the orbital phase winding of π . HQV d //x is preferred energetically. S.B. Chung , Bluhm, Kim, Vakaryuk, Leggett, PRL 99 , 197002 (2007). PRL 103, 057003 (2009).

Chiral p -wave state of Sr 2 RuO 4 cf.) s -wave Chiral p -wave Δ ( k ) ∝ k x + ik y ＋    0 ＋ ∝ e i  k       ＋ ＋ ＋ 0 0 Thus  (phase) =  k (direction) ＋       0 2 i  s -wave (with vortex)      － ＋ 0     i - i 2 k y         － ＋ 2  0   k x  - i 2    

H. Kaneyasu and M. Sigrist, arXiv: 1002.4793v2. T c (Sr 2 RuO 4 ) = 1.5 K T c (Ru) = 0.49 K At lower T , a vortex should be induced in Ru.

Anomalous I c – T of Pb/Sr 2 RuO 4 /Pb junction ■ Experimental study R. Jin et al. , PRB 55 , 4433 (1999). PSU T c,SRO 0.8 current source I c (mA) V 0.4 Pb Pb 0 2 4 6 T (K) The critical current I c is suppressed just below T c.SRO Interference between the superconductivities of Pb and Sr 2 RuO 4

Proximity effect in Pb/Sr 2 RuO 4 /Pb junction ■ Theoretical study Honerkamp & Sigrist Prog. Theor. Phys. 100 , 53 (1998). ● Pb : s -wave SC ( T c = 7.2 K ) Also by Yamashiro, Kashiwaya, and Tanaka. ＋ ＋ Pb Pb c Sr 2 RuO 4 0-junction 1.5 K < T < 7.2 K ＋ ＋ Pb Pb c - i － ＋ － i Sr 2 RuO 4 unstable stable T 1.5 K ＜

Important roles of Ru In Jin’s experiments, Pb Pb the crystals were not pure Sr 2 RuO 4 c but Sr 2 RuO 4 -Ru eutectic crystal . Ru 共晶 Sr 2 RuO 4 Low contact resistance between Pb and Ru allows the penetration of s -wave SC (Pb) into Ru, and then into Sr 2 RuO 4 A complication: the 3-K superconductivity .

3-K phase superconductivity Sr 2 RuO 4 -Ru eutectic system (3-K phase) 1.2 c 1.0 d V /d I (m  ) 0.8 Onset of the 0.6 400 Oe single-component 10 p -wave. 0.4 μ m 1000 Oe 0 Oe 0.2 Ru Sr 2 RuO 4 0 0 1 2 3 4 5 T (K) Onset of bulk sc. Onset of chiral sc: Expansion of the 3-K sc into the bulk.

Interference well-reproduced in micro-fabricated junctions The location of a pair of Ru inclusions The proximity are precisely known. Pb effect channel Width : 0.5 μ m Sr 2 RuO 4 Nakamura, Nakagawa et al. 100 μ m T c of Sr 2 RuO 4 I c1 I c2 I

Two I c ’s: Only one Pb is sufficient ! 10  A-rms 887 Hz I Left I Right Bridging T = 1.59 K V Left V Right V SRO V Left-Right = V Left-SRO + V SRO-Right 1 peak 1 peak 2 peak We need to re-consider the previous interpretation, since only one Pb is needed.

Pb/Ru/Sr 2 RuO 4 junction Measurement Apply Measure current I = I DC + I AC V = V AC source V ( I DC >> I AC ) ~1 mm

0.75 K 6.9 K Pb/Ru/Sr 2 RuO 4 junction V T c,SRO T (K) I c (mA) current source

Sr 2 RuO 4 and the 3-K phase k -dependence spatial dependence non chiral p -wave Sr 2 RuO 4 -Ru k x － ＋ eutectic system ( T < 3 K ) chiral p -wave Around the Sr 2 RuO 4 -Ru k x +  ik y interface ＋ － ( T < 2.4 K ) Phase winding: N = 0 － ＋ Sr 2 RuO 4 － ＋ chiral p -wave Ru i － ＋ k x + ik y － ＋ - i homogeneous in bulk Sr 2 RuO 4 Phase winding: N = 1

Conclusions 1. Pb/Ru/Sr 2 RuO 4 proximity junctions reveal the interference between s -SC and Sr 2 RuO 4 . 2. The unusual I c ( T ) is ascribable to the change in the phase windings around Ru. “Topological quantum phenomenon” 3. Further tests needed to prove Odd Parity of Sr 2 RuO 4 : ◆ Direct observation of induced vortex in Ru.