Giant enhancement of critical current density at high field in superconducting (Li,Fe)OHFeSe films by Mn doping

Abstract

Critical current density (Jc) is one of the major limiting factors for high field applications of iron-based superconductors.Here, we report that Mn-ions are successfully incorporated into nontoxic superconducting (Li,Fe)OHFeSe films.Remarkably, the Jc is significantly enhanced from 0.03 to 0.32 MA/cm 2 under 33 T, and the vortex pinning force density monotonically increases up to 106 GN/m 3 , which is the highest record so far among all iron-based superconductors. Our results demonstrate that Mn incorporation is an effective method to optimize the performance of (Li,Fe)OHFeSe films, offering a promising candidate for high-field applications.Recently, elemental Mn has been incorporated into FeSe-11111 single crystals without obvious detriment to its Tc [20], which may provide an effective candidate. Moreover, iron-based superconductors in the form of films usually present a higher Jc than that of bulk samples [6,8].Therefore, it is worthy introducing transition metal ions into FeSe-11111 crystalline superconducting film for further optimization of their high-field performance.In this letter, we successfully introduced Mn-ions into a superconducting FeSe-11111 film synthesized through the so-called 2 matrix-assisted hydrothermal epitaxy (MHE) method [12]. A significant enhancement of Jc was observed in FeSe-11111 films by Mn-doping, increasing it tenfold from 0.03 to 0.32 MA/cm 2 under 33 T at 5 K. Remarkably, the vortex pinning force density (Fp) of Mndoped films monotonically increases to 106 GN/m 3 . To the best of our knowledge, this is the highest record so far among all iron-based superconducting systems. By analyzing Fp versus magnetic fields, we find the apparent enhancement of Jc in the Mn-doped FeSe-11111 film stems from the extra pinning centers induced by Mn doping. ExperimentsThe pure and Mn-doped FeSe-11111 films were synthesized via the MHE method that we developed [12]. The x-ray diffraction (XRD) experiments were carried out on a 9 kW Rigaku SmartLab X-ray diffractometer. The scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy measurements were performed on a Hitachi SU5000. The electron energy loss spectroscopy (EELS) data were acquired using a transmission electron microscope (ARM200F, JEOL Inc.) equipped with a Gatan Quantum ER 965 Imaging Filter. Electrical transport measurements within 9T were collected with the standard four-probe method on a Quantum Design PPMS-9 system. The values of Jc were obtained using the criteria of 1 μV on I-V curves and the parameters of bridge were characterized by SEM. The high-field experiments up to 33 T were performed on the Steady High Magnetic Field Facilities, High Magnetic Field Laboratory, CAS.

Doping effects of transition metals on the superconductivity of (Li,Fe)OHFeSe films*

“…High-T c (42 K) FeSe-based compound (Li,Fe)OHFeSe [1] has received extensive attention because of the rich physics in the superconducting (SC) and normal states [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] as well as the potential for application. [19][20][21][22][23][24][25] The intercalated (Li,Fe)OHFeSe, sharing a similar electronic structure [7,8] with the prototypal FeSe monolayer, exhibits a strong electronic two-dimensionality and a nearly linear magnetic susceptibility extracted for the iron planes, [5] supporting the presence of magnetic fluctuations further evidenced by the inelastic neutron scatterings. [12,13] Recently, the Majorana zero bias mode [20] with quantized conductance plateau [21] is reported in the system.…”

“…On the other hand, the high-field critical current density (J c ) is observed to be remarkably enhanced by Mn doping. [24] So far most studies are focused on the physics related to the superconducting FeSe layers, with less attention paid on the intercalated (Li,Fe)OH layers. Previous results have shown that the Mn doping can affect the superconducting critical temperature (T c ) to certain extent in the (Li,Fe)OHFeSe single crystals.…”

A disorder-sensitive emergent vortex phase identified in high-T c superconductor (Li,Fe)OHFeSe

“…This is detrimental to potential highfield applications of the high-Tc superconductivity. Fortunately, we have checked that the exotic intermediate vortex phase can be eliminated by introducing the transition metal Mn into the crystal structure, as done in our previous studies [31,47]: Doping Mn into (Li,Fe)OHFeSe films yields the common vortex phase diagram shown in figure 4(b). Meanwhile, the critical current density is strongly enhanced in the Mn-doped (Li,Fe)OHFeSe films compared to the undoped ones, and Tc can also be kept at a high value of 36.6 K [31].…”

“…All samples were measured with the standard four-probe method. Part of the samples were patterned with a microbridge to determine Jc [31]. b.…”

Quasi-Two-Dimensional Nature of High-T c Superconductivity in Iron-Based (Li,Fe)OHFeSe

“…The self-field 𝐽c at 𝑇 = 2 K increases from 0.045 MA/cm −2 in FeSe to 1.9 MA/cm −2 in (Li,Fe)OHFeSe, indicating a high 𝐽c value achievable in high-𝑇c (Li,Fe)OHFeSe. [48,62] We note that, distinct from a monotonic 𝐽c variation of FeSe, 𝐽c of (Li,Fe)OHFeSe shows a local maximum 𝐽𝑐,max(𝐻, 𝑇 ) at a given 𝐻 and 𝑇 [see inset of Fig. S1(d)].…”