Upper critical field, temperature dependence

Fig. 20. (a) Temperature dependence of the upper critical field calculated within a two-band model for several impurity scattering rates yjmp (cm-1). (b) calculated Hc2(0)-vi.-ylmp curve illustrating the transition from the clean to the dirty limit. Dotted line Hc2(0)-y,mp dependence in the dirty limit. (Drechsler et al. 2000 Fuchs... 

Fig. 46. Temperature dependence of the upper critical field Hcj for TmNiil C and ErNi2B2C single crystals. Circles H a. triangles H c (after Canfield and Bud ko 2001).

Fig. 60. Concentration dependence of various properties of polycrystalline Y(Ni xPt )2B2C obtained by specific heat measurements transition temperature Tc exponent a and parameter Hc2 from eq. (6) upper critical field Hc2(0) at T =0, where the dotted line schematically describes the dirty limit corresponding to the isotropic single band case (in reality there is a finite intersection with the field-axis for the dotted asymptotic line, see Shulga and Drechsler 2002) exponent fi of eq. (8) for the curvature of the electronic specific heat in the mixed state and Sommerfeld constant xn (after Lipp et al. 2001).

Fig. 63. Temperature dependence of the upper critical field, HC2(T), (a) of YNi2B2C and Tby Yq 9Ni2B2C and (b) of Tby i Y0 8N12B2C single crystals for two directions of the applied magnetic field W (001) (closed squares) and //11[ 100] (open squares), alter Bitterlich et al. (2001).

Summary. On the basis of phenomenological Ginzburg-Landau approach we investigate the problem of order parameter nucleation in a ferromagnetic superconductor and hybrid superconductor - ferromagnetic (S/F) systems with a domain structure in an applied external magnetic field H. We study the interplay between the superconductivity localized at the domain walls and between the domain walls and show that such interplay determines a peculiar nonlinear temperature dependence of the upper critical field. For hybrid S/F systems we also study the possible oscillatory behavior of the critical temperature TC(H) similar to the Little-Parks effect. 

The goal of the present paper is to study the unusual nonlinear behavior of the temperature dependence of the upper critical field observed experimentally in hybrid S/F systems and ferromagnetic superconductors using the GL model. We consider a linearized GL equation which is equivalent to... 

In contrast to the conventional s-wave superconductor picture above, Gasparov et al. (2006) report unusual temperature dependence of the magnetic penetration depth A.(T) and upper critical field Hc2(T) and propose that ZrBi2 has an unconventional two-gap superconductivity. 

FIGURE 24 The temperature dependence of the upper critical field of an YNi2B2C thin film, resistively measured in the principal crystallographic directions (from Wimbush et al., 2004b). 

FIGURE 27 The temperature dependence of the upper critical field of YNi2B2C measured by susceptibility with applied field parallel to c at ambient pressure, 2.3, 3.3, 5.4,7.6, 9.0, and 11.7 GPa (from top to bottom). The solid lines correspond to two-band fits (after Suderow et al., 2004). 

Fig. 2.26. Temperature dependence of the upper critical field of 0-(ET)2l3 along three directions determined by resistivity measurements. FYom [190]...

Fig. 2.30. Temperature dependence of the upper critical fields of (a) k-(ET)2-Cu(NCS)2 and (b) ft-(ET)2Cu[N(CN)2]Br extracted from magnetization measurements. Prom [189]...

We have measured the temperature dependence of the lower and upper critical fields in superconducting KjCso. From the measurements, we have evaluated the jwnetration depth (X 2400 A) and superconducting coherence length ( 26 A). The parameters are in agreement with a superconducting state formed by a narrow band. 

The upper critical field HdiT) was evaluated from the temperature dependence of the field-cooled magnetization. From the normal phase, the sample was cooled to the superconducting state in an external magnetic field (2 kOc < //ext < 50 kOe). We monitored the magnetization while heating the sample until the normal state is reached, with the applied field held constant. The intercept of a linear extrapolation of the magnetization in the superconducting state with the normal-state base line defines the transition temperature T, and the upper critical field Hci(,T) is equal to the applied field. 

In Fig. 3 we have plotted the temperature dependence of the upper and lower critical fields, determined as described earlier. For the upper critical field we observe that, except in the vicinity of the critical temperature... 

FIG. 3. (a) The temperature dependence of the lower critical field //, ifT) determined on a powder sample as shown in the inset and explained in the text. Error bars represent estimated uncertainty in determining H . The solid line represents the empirical law //, i(7 )/W, i(0) 1 —(T/T, ). (b) The temperature dependence of the upper critical field H, i(T). Inset The method of determining these values from M(T) curves at fixed field. The error bars in the main plot reflect the round-... 

Critical current density also depends on magnetic field, decreasing monotonically to zero at the upper critical field Hc2 (16-17). In YBaCuO the slope of Hc2 with temperature is unusually large, of order 2 T/K when field is applied parallel to the predominant conduction planes of the structure (18-19). This implies record values (up to 200 T has been estimated) for the upper critical field at low temperatures and opens up the possibility of very high field magnets. 

Figure 2. Schematic temperature dependence of the upper critical field, H. . The dashed curves are not experimentally observable. Is the field parallel to the...

Figure 2. Temperature dependence of the upper critical fields for the samples with dcUNi= 4 nm (a) and dcuNi= 6 nm (b). The solid lines indicate the 2D theoretical fit for Hc2ii. The dotted lines the linear fit of HC2 .

Fig. 85. Temperature dependence of the upper critical field of UPt, for three values of the applied hydrostatic pressure in the regime near TXp = 0, B = 0) and for a field in the basal plane. Note the complete disappearance of the sharp break in slope of 0.4 T in going from ambient pressure to p = 1.4 kbar. This suggests a very rapid suppression of phase A (cf. fig. 83) under pressure (Taillefer 1990).

Upper Critical Field r2b.i.p1. The early data of the temperature dependence of the upper critical field of the H salt (magnetic field < 13.5 Tesla) showed an inflection at around 9 K, and Hc2 exceeded 13 Tesla at 5 K within the 2D plane (Fig. 14). H. 2 measurements at higher magnetic fields, up to 24 Tesla, indicate that 11 2, estimated at 0.5 K in the bc-plane, exceeds the Pauli limiting value (Hp) [30] ... 

Fig. 8 shows the temperature dependence of the upper critical field for crystals of at-(BEDT-TTF)2l3, for the magnetic field perpendicular and parallel to the c -axis. It can clearly be seen that, for the region T / T, > 0.65 (T = 8 K), the crystals behave as isotropic... 

The upper critical field exceeds the Chandrasekhar-Clogston limit by 25% at 0.3 K and fields parallel to the cation layers (b axis), and shows an anomalously large temperature dependence at low temperatures. 

---