本文選題：反鐵磁體 + 非常規(guī)超導體　； 參考：《浙江大學》2015年博士論文

【摘要】：超導電性是凝聚態(tài)物理的重要領域,而探索新超導材料又是超導研究的一個重要方向。Onnes發(fā)現(xiàn)超導電性之后,BCS理論在解釋基于電聲子耦合的常規(guī)超導體上獲得了成功。但是,每一類非常規(guī)超導體的發(fā)現(xiàn),如重費米子、銅氧化物和鐵基等非常規(guī)超導體,都對該體系的超導理論提出了重大的挑戰(zhàn)。在常規(guī)超導體中,磁性會破壞超導Cooper對而不利于超導,而在非常規(guī)超導體中,超導Cooper對可能跟磁性密切相關。盡管不同的非常規(guī)超導體的超導機理可能不盡相同,但是它們都有個相似的相圖：利用某種手段將體系的磁性壓制之后超導才出現(xiàn)。本論文借鑒非常規(guī)超導體相似的相圖,設想通過化學摻雜壓制化合物的反鐵磁序來探索超導電性。本論文結合當前的研究背景,嘗試對三個反鐵磁體BaFe2Se3,BaMn2As2和BaCr2As2的鉀摻雜效應進行研究,所取得的創(chuàng)新成果如下：(1) BaFe2Se3是一個反鐵磁絕緣體,而所有鉀摻雜的樣品都呈現(xiàn)出絕緣體性質。我們對其中一個鉀摻雜量的樣品Ba0.6K0.4Fe2Se3進行了細致的物理性質表征,包括各向異性電阻和磁化率以及比熱。Ba0.6K0.4Fe2Se3的電阻率具有弱的各向異性,低溫下呈現(xiàn)可變程跳躍電導。我們發(fā)現(xiàn)Ba0.6K0.4Fe2Se3是一個具有各向異性的Heisenberg型自旋玻璃體。(2) BaMn2As2摻鉀之后,體系從絕緣體變?yōu)榻饘�。目前的鉀摻雜量不能完全壓制母體的G型反鐵磁,暫時還沒有在該體系實現(xiàn)超導電性。我們對組分為x＝0.19和x=0.26的Ba1-xKxMn2As2做了電阻和各向異性磁化率的測量,首次發(fā)現(xiàn)了30-50 K左右的弱鐵磁轉變。體系弱鐵磁的易磁化軸沿著ab面,而G型反鐵磁的磁矩沿著c方向。我們發(fā)現(xiàn)x=0.19和x=0.26樣品ab面的磁化率符合奇異的居里外斯行為,其中有效磁矩相當于自旋為1/2的順磁體。我們對母體和x=0.25的樣品進行了第一性原理計算,表明鉀摻雜之后As的4p空穴占金屬導電的主要部分。我們對該體系中出現(xiàn)弱鐵磁性進行了兩種可能性的討論：一種是載流子的自旋發(fā)生極化而出現(xiàn)弱鐵磁,另一種是G型反鐵磁的磁矩沿著ab面發(fā)生傾斜而出現(xiàn)鐵磁分量。(3) BaCr2As2的鉀摻雜樣品的合成并不成功,但是我們發(fā)現(xiàn)了兩個新的準一維化合物K2Cr3As3和KCr3As3。它們由(Cr3As3)∞一維鏈和鉀離子填充而成。我們首次發(fā)現(xiàn)鉻基砷化物K2Cr3As3在常壓下具有6.1 K超導電性,是一個極端的Ⅱ類超導體。多晶樣品正常態(tài)電阻和溫度呈現(xiàn)線性依賴關系,暗示非費米液體行為。K2Cr3As3具有較高的上臨界場,是Pauli順磁極限(Hp=11 T)的3-4倍,暗示自旋三重態(tài)配對的可能性。它具有較大的正常態(tài)電子比熱(γ=70-75 mJ K-2)和比熱跳變(等=2.2-2.4),表明體系處于較強的電子關聯(lián)和強耦合的情況。上述結果強烈指向K2Cr3As3具有非常規(guī)超導電性。在K2Cr3As3基礎上,利用酒精退去其中的一個鉀,我們合成了新的化合物KCr3As3。電阻、磁化率和比熱測量表明KCr3As3并不超導。KCr3As3電阻低溫下呈現(xiàn)半導體行為,但是電阻變化不大。KCr3As3磁化率高溫下呈現(xiàn)出居里外斯行為,鉻的有效磁矩為0.68 μB/Cr。直流和交流磁化率證實KCr3As3低溫下呈現(xiàn)集團自旋玻璃態(tài)。盡管KCr3As3并不超導,但是對于它的研究同樣有助于理解K2Cr3As3的超導電性。此外,在論文的最后一章提到了后續(xù)工作的展望。
[Abstract]:Superconductivity is an important field in condensed matter physics. While exploring new superconducting materials is an important direction in the study of superconductivity,.Onnes finds superconductivity, and BCS theory has been successful in interpreting conventional superconductors based on electroacoustic coupling. However, the discovery of each kind of unconventional superconductor, such as heavy fermion, copper oxide and iron base, has been found. Unconventional superconductors have made great challenges to the superconducting theory of the system. In conventional superconductors, magnetic properties will destroy superconducting Cooper pairs and are not conducive to superconductivity. In unconventional superconductors, superconducting Cooper is likely to be closely related to magnetism. Although the superconducting mechanisms of different unconventional superconductors may vary, they are different There is a similar phase diagram: the magnetic suppression of the system is made by some means. In this paper, we use the similar phase diagram of the unconventional superconductor to explore the superconductivity by the antiferromagnetic order of chemical doping to suppress the compounds. This paper tries to use three antiferromagnets, BaFe2Se3, BaMn2As2, in combination with the current research background. The effects of potassium doping on BaCr2As2 are studied. The results obtained are as follows: (1) BaFe2Se3 is an antiferromagnetic insulator, and all potassium doped samples show insulators. We have detailed characterization of the physical properties of one of the potassium doped samples, Ba0.6K0.4Fe2Se3, including anisotropic resistance and magnetization. The resistivity of the ratio and the specific heat.Ba0.6K0.4Fe2Se3 has a weak anisotropy, and the variable range jump conductance is presented at low temperature. We found that Ba0.6K0.4Fe2Se3 is an anisotropic Heisenberg type spin vitreo. (2) after the BaMn2As2 is doped with potassium, the system becomes metal from the insulator. The current potassium content can not completely suppress the G type of the parent body. Antiferromagnetic, for the time being, we have not yet achieved superconductivity in this system. We have measured the resistance and anisotropic susceptibility to the Ba1-xKxMn2As2 of x = 0.19 and x=0.26, and we first found a weak ferromagnetic transition about 30-50 K. The susceptibility of the weak ferromagnetic system along the AB surface and the G type antiferromagnetic magnetic moment along the c direction. We found x=0.19. The magnetization of the AB surface of the x=0.26 sample and the sample of the x=0.26 conforms to the singular Curie's behavior, in which the effective magnetic moment is equivalent to the paramagnetic of the spin of 1/2. We have carried out the first principle calculation of the samples of the mother and x=0.25, indicating that the 4P vacancy of As is the main part of the metal conduction after the potassium doping. We have carried out two of the weak ferromagnetism in the system. The discussion of the possibility: one is the spin polarization of the carrier and the presence of weak ferromagnetism, the other is that the G type antiferromagnetic moment inclines along the AB surface and appears ferromagnetic component. (3) the synthesis of potassium doped samples from BaCr2As2 is not successful, but we found that two new quasi one-dimensional compounds, K2Cr3As3 and KCr3As3., are (Cr3As3). It is the first time to find that the chromatid arsenide K2Cr3As3 has 6.1 K superconductivity at atmospheric pressure, and is an extreme class II superconductor. The normal resistance and temperature of the polycrystalline samples show a linear dependence, suggesting that the non Fermi liquid behavior.K2Cr3As3 has a higher critical field and is a Pauli paramagnetic limit (Hp=1 1 T) 3-4 times, suggesting the possibility of pairing spin three heavy states. It has a larger normal electronic specific heat (gamma =70-75 mJ K-2) and specific thermal jump (=2.2-2.4), indicating that the system is in strong electron correlation and strong coupling. The above results strongly point to K2Cr3As3 with unconventional superconductivity. On the basis of K2Cr3As3, alcohol is withdrawn. One of the potassium, we synthesized a new compound KCr3As3. resistance, the susceptibility and specific heat measurements showed that KCr3As3 did not exhibit semiconductor behavior at low temperature at low temperature, but the resistance changed little.KCr3As3 magnetic susceptibility at high temperature, showing Curie's behavior, the effective magnetic moment of chromium was 0.68 mu B/Cr. DC and AC susceptibility confirmed. KCr3As3 presents a group spin glass state at low temperatures. Although KCr3As3 is not superconducting, the study of it also helps to understand the superconductivity of K2Cr3As3. In addition, in the last chapter of the paper, the prospect of follow-up work is mentioned.

【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：O469;O511.3

【參考文獻】

相關期刊論文 前1條

1 湯章圖;鮑金科;王震;白樺;蔣好;劉藝;翟會飛;馮春木;許祝安;曹光旱;;長鏈間距準一維Cs_2Cr_3As_3中的超導電性（英文）[J];Science China Materials;2015年01期

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本文編號：1881729