π-d interaction in the field induced superconductor λ-(BETS)2FeCl4: Studied by77Se NMR

Solid-state selenium-77 NMR

“…Under ambient pressure, k-(BETD-TSF) 2 FeCl 4 shows a metal-insulator transition at T MI = 8 K. External applied magnetic fields reduce T MI and solid-state 77 Se NMR evidence for this transition has been found at 3.5 K when B 0 = 9.0 T [177], and 1.6 K when B 0 = 11.7 T [178]. At magnetic field strengths greater than 18 T, k-(BETD-TSF) 2 FeCl 4 undergoes field-induced superconductivity, FISC, reaching a maximum T c = 4.2 K at B 0 = 33 T, and with even greater magnetic fields T c returns to 0 K around B 0 = 45 T. Solid-state 77 Se NMR measurements were able to provide the first direct evidence of strong coupling between the conduction p electrons and the Fe d electron spins in k-(BETD-TSF) 2 FeCl 4 [166,177,179,180], and another FISC j-(BETD-TSF) 2 FeBr 4 [181,182]. This evidence has been used to elucidate the nature of the FISC state in these materials.…”

“…In 1962, Jaccarino and Peter [183] predicted a FISC state when the external field is able to cancel the exchange field from the Fe moments. The high-field solid-state 77 Se NMR studies on (BETD-TSF) 2 FeX 4 FISCs have been interpreted as providing evidence for this Jaccarino-Peter compensation mechanism [166,177,179,180,182]. Fig.…”

Multifunctional interplay among the conductivity, magnetism and dielectricity in π–d interacting λ-(BETS)2FeCl4

“…As a consequence, a charge ordering [55] is discussed as a possible cause for the splitting of the proton resonance below T FM . To note, this speculation is also supported by recent 13 C NMR measurements [56] detecting the anomalous line broadening. Taking into account the heterogeneous state speculated from the anomalous microwave conductivity, it may be reasonable to suppose that a uniform metallic state could change into some phase-separated state in which a domain pattern consisting of metallic and dielectric regions might appear.…”

Microscopic Observation of π Spin Polarization by d Localized Spin in λ Type BETS Based Organic Superconductors

“…The explanation of this unusual phenomenon is the compensation mechanism [9]: polarized 3d electrons produce a strong magnetic field through the exchange interaction with π conduction electrons, which cancels the applied field. The magnitude of the exchange field by localized d spin was evaluated experimentally and the compensation mechanism was evidenced by several studies [5,10,11] including our NMR studies [12,13]. The details of the FISC of the system were reviewed by Uji and Brooks [14].…”