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Magnetic flux quantum

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The phenomenon of flux quantization was first discovered in superconductors experimentally by B. S. Deaver and W. M. Fairbank and, independently, by R. Doll and M. Näbauer, in 1961. The quantization of magnetic flux is closely related to the
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and, correspondingly, will not change any physical properties. However, in the superconductor of non-trivial topology, e.g. superconductor with the hole or superconducting loop/cylinder, the phase
896: 1496:. The normal core plays a role of a hole in the superconducting phase. The magnetic field lines pass along this normal core through the whole sample. The screening currents circulate in the 569:
of the irradiation. The Josephson effect is very widely used to provide a standard for high-precision measurements of potential difference, which (from 1990 to 2019) were related to a fixed,
1180: 934: 2110:"The Feynman Lectures on Physics Vol. III Ch. 21: The Schrödinger Equation in a Classical Context: A Seminar on Superconductivity, Section 21-7: Flux quantization" 1416:
only when the path/trajectory around the hole described above can be chosen so that it lays in the superconducting region without screening currents, i.e. several
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To understand this definition in the context of the Dirac flux quantum one shall consider that the effective quasiparticles active in a superconductors are
2036:"Quantized Magnetic Flux in Superconductors: Experiments confirm Fritz London's early concept that superconductivity is a macroscopic quantum phenomenon" 1274: 1099: 1567:
is generally associated with the behaviour of microscopically small systems, whereas the quantization of magnetic flux in a superconductor and the
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Deaver, Bascom; Fairbank, William (July 1961). "Experimental Evidence for Quantized Flux in Superconducting Cylinders".
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Now, because the order parameter must return to the same value when the integral goes back to the same point, we have:
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away from the surface. There are geometries where this condition cannot be satisfied, e.g. a loop made of very thin (
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consists of a normal core—a cylinder of the normal (non-superconducting) phase with a diameter on the order of the
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can be as well but increments of flux can be quantized. The wave function can be multivalued as it happens in the
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Doll, R.; Näbauer, M. (July 1961). "Experimental Proof of Magnetic Flux Quantization in a Superconducting Ring".
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have fixed values, and the Josephson effect along with the von Klitzing quantum Hall effect becomes the primary
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as one goes around the hole/loop and comes to the same starting point. If this is so, then one has
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The first to realize the importance of the flux quantum was Dirac in his publication on monopoles
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Loder, F.; Kampf, A. P.; Kopp, T.; Mannhart, J.; Schneider, C. W.; Barash, Y. S. (2008).
1568: 2012: 1977: 1942: 1805: 2305: 2071: 1928: 1857: 1760: 1572: 2063: 2055: 1834: 1750: 1628: 1409:-layer) will always be quantized. However, the value of the flux quantum is equal to 2274: 2075: 2047: 2016: 1981: 1946: 1809: 1529: 1506: 1483: 1479: 725: 558: 2109: 2051: 1886: 2090: 1745: 1710: 1553: 1341: 729: 474: 465: 133: 1528:, the magnetic flux quantum was measured with great precision by exploiting the 2203: 2174: 1755: 1576: 628: 419: 415: 2289: 2059: 2020: 1985: 75: 2067: 1916: 1813: 1725: 1450: 527: 486: 369: 309: 1369:
and usually ≈ 100 nm). The screening currents also flow in this
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inside the superconductor, which perfectly compensates the applied field
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The following physical equations use SI units. In CGS units, a factor of
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If one deals with a superconducting ring (i.e. a closed loop path in a
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for the definition of the ampere and other electric units in the SI.
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for the definition of the ampere and other electric units in the SI"
1624: 1331:{\displaystyle \Phi _{B}={\frac {\hbar }{q}}2\pi ={\frac {h}{2e}}.} 295:{\displaystyle \Phi _{0}={\frac {2\pi \hbar c}{q}}={\frac {hc}{q}}} 1933: 84:, threading some contour or loop is defined as the magnetic field 1456:
Flux quantization also plays an important role in the physics of
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inside the superconductor is zero. More exactly, magnetic field
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magnetic flux quanta trapped in the hole/loop, as shown below:
647:— the superconducting order parameter. As any complex function 1356:
penetrates into a superconductor over a small distance called
422:, the magnetic flux threading such a hole/loop is quantized. 1620: 1446: 482:. Its value is, therefore, the same for any superconductor. 402: 2144: 1917:"Magnetic flux periodicity of h/E in superconducting loops" 1092:
Inside the body of the superconductor, the current density
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is the charge of the Cooper pair. The wave function is the
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The phenomenon of flux quantization was predicted first by
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R. Shankar, "Principles of Quantum Mechanics", eq. 21.1.44
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obtained until 2019. This may be counterintuitive, since
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Plugged into the expression of the current, one obtains:
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is a combination of fundamental physical constants: the
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and later discovered experimentally in superconductors (
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The NIST Reference on Constants, Units, and Uncertainty
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The NIST Reference on Constants, Units, and Uncertainty
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The NIST Reference on Constants, Units, and Uncertainty
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The NIST Reference on Constants, Units, and Uncertainty
1957: 1914: 1790:"Quantised Singularities in the Electromagnetic Field" 1277: 1188: 1154: 1102: 1019: 937: 904: 742: 495: 239: 175: 2092:
Superfluids: Macroscopic theory of superconductivity
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The superconducting properties in each point of the
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may be too technical for most readers to understand
1400:The magnetic flux frozen in a loop/hole (plus its 1330: 1261: 1174: 1134: 1082: 1003: 919: 891:{\displaystyle \mathbf {J} ={\frac {1}{2m}}\left.} 890: 510: 294: 222: 2095:. John Wiley & Sons. pp. 152 (footnote). 2287: 1852: 1850: 1552:, this provided the most accurate values of the 1378:-layer near the surface, creating magnetization 586:, the Josephson constant has an exact value of 557:. It is the constant of proportionality of the 136:. The unit of quantization is therefore called 1963: 1826: 1519: 614:Derivation of the superconducting flux quantum 143: 1847: 1445:The flux quantization is a key idea behind a 1716:Committee on Data for Science and Technology 1615:which, together with the definitions of the 1175:{\displaystyle \nabla \times \mathbf {A} =B} 2196: 2167: 1998: 1879: 1532:. When coupled with the measurement of the 1858:"2022 CODATA Value: magnetic flux quantum" 1623:, provides the official definition of the 2262:and flux quantization in superconductors 1932: 1658:. Therefore, both the Josephson constant 1358:London's magnetic field penetration depth 973: 59:Learn how and when to remove this message 43:, without removing the technical details. 695:may continuously change from some value 489:with an effective charge of 2 electrons 122:can be arbitrary, meaning that the flux 1887:"2022 CODATA Value: Josephson constant" 1144:Integrating around the hole/loop using 2288: 2204:"2022 CODATA Value: elementary charge" 2088: 1820: 2104: 2102: 2033: 1784: 1509:carries one quantum of magnetic flux 1449:, which is one of the most sensitive 327:Superconducting magnetic flux quantum 41:make it understandable to non-experts 2175:"2022 CODATA Value: Planck constant" 15: 1830:Introduction to Solid State Physics 573:of the Josephson constant, denoted 565:across a Josephson junction to the 13: 2253: 2099: 1794:Proceedings of the Royal Society A 1279: 1237: 1190: 1155: 1103: 1043: 938: 865: 832: 825: 810: 804: 798: 777: 241: 177: 14: 2322: 1833:. Wiley & Sons. p. 281. 1119: 1059: 822: 795: 674:is the phase. Changing the phase 635:quantum mechanical wave function 537:The inverse of the flux quantum, 262: 198: 1494:superconducting coherence length 1252: 1217: 1206: 1162: 1125: 1065: 1021: 989: 964: 945: 856: 744: 20: 2225: 2158: 2126: 929:Ginzburg–Landau order parameter 526:, but was predicted earlier by 71:Quantized unit of magnetic flux 2082: 2027: 1908: 1778: 1675:and the von Klitzing constant 1469:and the second critical field 993: 985: 968: 960: 949: 941: 870: 861: 828: 813: 801: 786: 1: 2052:10.1126/science.146.3650.1429 1771: 1741:Macroscopic quantum phenomena 1579:large numbers of particles. 152:Dirac magnetic flux quantum 90:multiplied by the loop area 78:, represented by the symbol 7: 2114:feynmanlectures.caltech.edu 2034:Parks, R. D. (1964-12-11). 1699: 1520:Measuring the magnetic flux 1397:inside the superconductor. 317: 144:Dirac magnetic flux quantum 10: 2327: 2233:"BIPM – mises en pratique" 1631:also has a fixed value of 736:in the superconductor is: 1344:, the magnetic induction 333: 161: 156: 2021:10.1103/PhysRevLett.7.51 1986:10.1103/PhysRevLett.7.43 2266:(physics stackexchange) 2001:Physical Review Letters 1966:Physical Review Letters 1827:C. Kittel (1953–1976). 1736:Husimi Q representation 1721:Domain wall (magnetism) 1584:2019 revision of the SI 1526:2019 revision of the SI 1458:type II superconductors 1096:is zero, and therefore 584:2019 revision of the SI 2089:London, Fritz (1950). 1814:10.1098/rspa.1931.0130 1731:Ginzburg–Landau theory 1586:, the Planck constant 1332: 1263: 1176: 1136: 1084: 1005: 921: 892: 532:phenomenological model 512: 425:The (superconducting) 418:) or a hole in a bulk 296: 224: 2272:David tong lectures: 1766:von Klitzing constant 1534:von Klitzing constant 1333: 1264: 1177: 1137: 1085: 1006: 922: 893: 668:is the amplitude and 631:are described by the 513: 427:magnetic flux quantum 297: 225: 138:magnetic flux quantum 2260:Aharonov–Bohm effect 1706:Aharonov–Bohm effect 1390:, thus resulting in 1275: 1186: 1152: 1100: 1017: 935: 920:{\displaystyle q=2e} 902: 740: 563:potential difference 511:{\displaystyle q=2e} 493: 314:Aharanov-Bohm effect 237: 173: 130:Aharonov–Bohm effect 2276:Quantum hall effect 2046:(3650): 1429–1435. 2013:1961PhRvL...7...51D 1978:1961PhRvL...7...43D 1943:2008NatPh...4..112L 1806:1931RSPSA.133...60D 1800:(821). London: 60. 1627:. Furthermore, the 1582:As a result of the 1569:quantum Hall effect 524:Little–Parks effect 153: 132:or quantized as in 2311:Physical constants 1761:Topological defect 1592:has a fixed value 1573:emergent phenomena 1480:Abrikosov vortices 1328: 1259: 1172: 1132: 1080: 1001: 917: 888: 651:can be written as 571:conventional value 546:Josephson constant 508: 292: 220: 151: 2301:Quantum magnetism 2296:Superconductivity 1840:978-0-471-49024-1 1751:Magnetic monopole 1629:elementary charge 1577:thermodynamically 1323: 1299: 1232: 1122: 1062: 1036: 971: 764: 548:, and is denoted 412: 411: 306: 305: 290: 272: 218: 205: 69: 68: 61: 2318: 2282: 2281: 2269: 2247: 2246: 2244: 2243: 2229: 2223: 2222: 2220: 2219: 2200: 2194: 2193: 2191: 2190: 2171: 2165: 2162: 2156: 2155: 2153: 2147:. Archived from 2142: 2136:Mise en pratique 2130: 2124: 2123: 2121: 2120: 2106: 2097: 2096: 2086: 2080: 2079: 2031: 2025: 2024: 1996: 1990: 1989: 1961: 1955: 1954: 1951:10.1038/nphys813 1936: 1912: 1906: 1905: 1903: 1902: 1883: 1877: 1876: 1874: 1873: 1854: 1845: 1844: 1824: 1818: 1817: 1782: 1694:mise en pratique 1691: 1674: 1653: 1650: 1648: 1645: 1642: 1637: 1614: 1612: 1610: 1607: 1604: 1598: 1591: 1575:associated with 1566: 1560: 1551: 1530:Josephson effect 1515: 1507:Abrikosov vortex 1504: 1491: 1484:Abrikosov vortex 1477: 1468: 1441: 1434: 1424: 1415: 1408: 1396: 1389: 1383: 1377: 1368: 1355: 1349: 1337: 1335: 1334: 1329: 1324: 1322: 1311: 1300: 1292: 1287: 1286: 1268: 1266: 1265: 1260: 1255: 1244: 1233: 1225: 1220: 1209: 1198: 1197: 1181: 1179: 1178: 1173: 1165: 1141: 1139: 1138: 1133: 1128: 1123: 1115: 1110: 1089: 1087: 1086: 1081: 1073: 1069: 1068: 1063: 1055: 1050: 1037: 1029: 1024: 1010: 1008: 1007: 1002: 997: 996: 992: 972: 967: 956: 948: 926: 924: 923: 918: 897: 895: 894: 889: 884: 880: 879: 878: 873: 864: 859: 845: 841: 840: 839: 785: 784: 765: 763: 752: 747: 726:minimal coupling 720: 716: 703: 694: 690: 687:will not change 686: 679: 673: 667: 660: 650: 646: 623: 609: 607: 604: 600: 591: 578: 559:Josephson effect 553: 544:, is called the 543: 530:in 1948 using a 517: 515: 514: 509: 481: 472: 463: 462: 459: 457: 453: 450: 444: 399: 396: 394: 390: 380: 366: 363: 361: 357: 354: 344: 331: 330: 322: 312:then within the 301: 299: 298: 293: 291: 286: 278: 273: 268: 254: 249: 248: 229: 227: 226: 221: 219: 211: 206: 201: 190: 185: 184: 154: 150: 127: 121: 115: 109: 95: 89: 83: 64: 57: 53: 50: 44: 24: 23: 16: 2326: 2325: 2321: 2320: 2319: 2317: 2316: 2315: 2286: 2285: 2279: 2273: 2263: 2256: 2254:Further reading 2251: 2250: 2241: 2239: 2231: 2230: 2226: 2217: 2215: 2202: 2201: 2197: 2188: 2186: 2173: 2172: 2168: 2163: 2159: 2151: 2140: 2132: 2131: 2127: 2118: 2116: 2108: 2107: 2100: 2087: 2083: 2032: 2028: 1997: 1993: 1962: 1958: 1913: 1909: 1900: 1898: 1885: 1884: 1880: 1871: 1869: 1856: 1855: 1848: 1841: 1825: 1821: 1783: 1779: 1774: 1746:Magnetic domain 1711:Brian Josephson 1702: 1682: 1676: 1665: 1659: 1651: 1646: 1643: 1640: 1638: 1632: 1608: 1605: 1602: 1600: 1594: 1593: 1587: 1562: 1556: 1554:Planck constant 1542: 1536: 1522: 1514: 1510: 1503: 1497: 1487: 1476: 1470: 1467: 1461: 1440: 1436: 1433: 1426: 1423: 1417: 1414: 1410: 1407: 1401: 1391: 1385: 1379: 1376: 1370: 1367: 1361: 1351: 1345: 1342:Meissner effect 1315: 1310: 1291: 1282: 1278: 1276: 1273: 1272: 1251: 1240: 1224: 1216: 1205: 1193: 1189: 1187: 1184: 1183: 1161: 1153: 1150: 1149: 1146:Stokes' theorem 1124: 1114: 1106: 1101: 1098: 1097: 1064: 1054: 1046: 1042: 1038: 1028: 1020: 1018: 1015: 1014: 988: 978: 974: 963: 955: 944: 936: 933: 932: 903: 900: 899: 874: 869: 868: 860: 855: 835: 831: 780: 776: 775: 771: 770: 766: 756: 751: 743: 741: 738: 737: 730:current density 718: 711: 705: 702: 696: 692: 688: 681: 675: 669: 666: 662: 656: 652: 648: 636: 619: 616: 605: 602: 598: 596: 594: 587: 581: 574: 561:, relating the 556: 549: 542: 538: 494: 491: 490: 477: 475:electron charge 468: 466:Planck constant 460: 455: 451: 448: 446: 434: 430: 429: 397: 392: 388: 386: 383: 376: 364: 359: 355: 352: 350: 347: 342: 329: 279: 277: 255: 253: 244: 240: 238: 235: 234: 210: 191: 189: 180: 176: 174: 171: 170: 146: 134:superconductors 123: 117: 111: 97: 91: 85: 79: 72: 65: 54: 48: 45: 37:help improve it 34: 25: 21: 12: 11: 5: 2324: 2314: 2313: 2308: 2303: 2298: 2284: 2283: 2270: 2255: 2252: 2249: 2248: 2224: 2195: 2166: 2157: 2154:on 2021-03-08. 2125: 2098: 2081: 2026: 1991: 1956: 1927:(2): 112–115. 1921:Nature Physics 1907: 1878: 1846: 1839: 1819: 1776: 1775: 1773: 1770: 1769: 1768: 1763: 1758: 1756:Quantum vortex 1753: 1748: 1743: 1738: 1733: 1728: 1723: 1718: 1713: 1708: 1701: 1698: 1680: 1663: 1654:to define the 1540: 1521: 1518: 1512: 1501: 1474: 1465: 1438: 1431: 1421: 1412: 1405: 1374: 1365: 1327: 1321: 1318: 1314: 1309: 1306: 1303: 1298: 1295: 1290: 1285: 1281: 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Retrieved 2237:www.bipm.org 2236: 2227: 2216:. Retrieved 2207: 2198: 2187:. Retrieved 2178: 2169: 2160: 2149:the original 2135: 2128: 2117:. Retrieved 2113: 2091: 2084: 2043: 2039: 2029: 2007:(2): 51–52. 2004: 2000: 1994: 1972:(2): 43–46. 1969: 1965: 1959: 1924: 1920: 1910: 1899:. Retrieved 1890: 1881: 1870:. Retrieved 1861: 1828: 1822: 1797: 1793: 1780: 1726:Flux pinning 1693: 1688: 1684: 1677: 1671: 1667: 1660: 1633: 1611:10 J⋅Hz 1595: 1588: 1581: 1563: 1557: 1548: 1544: 1537: 1523: 1498: 1488: 1471: 1462: 1455: 1444: 1428: 1418: 1402: 1399: 1392: 1386: 1380: 1371: 1362: 1352: 1346: 1339: 1270: 1143: 1093: 1091: 1012: 734:Cooper pairs 723: 713: 706: 697: 683: 676: 670: 657: 642: 638: 632: 626: 620: 617: 588: 582:. With the 575: 550: 545: 536: 528:Fritz London 520: 487:Cooper pairs 484: 478: 469: 440: 436: 426: 424: 413: 377: 310:Fritz London 307: 233: 169: 147: 137: 124: 118: 112: 106: 102: 98: 92: 86: 80: 73: 55: 46: 30: 1786:Dirac, Paul 1453:available. 1340:Due to the 2290:Categories 2242:2020-01-21 2218:2024-05-18 2214:. May 2024 2189:2024-05-18 2185:. May 2024 2119:2020-01-21 1901:2024-05-18 1897:. May 2024 1872:2024-05-18 1868:. May 2024 1772:References 458:10 Wb 49:April 2024 2306:Metrology 2060:0036-8075 1934:0709.4111 1649:10 C 1571:are both 1360:(denoted 1305:π 1294:ℏ 1280:Φ 1246:⋅ 1242:θ 1238:∇ 1235:∮ 1227:ℏ 1211:⋅ 1203:∮ 1191:Φ 1159:× 1156:∇ 1120:ℏ 1108:θ 1104:∇ 1075:ρ 1060:ℏ 1052:− 1048:θ 1044:∇ 1031:ℏ 983:θ 958:ρ 939:Ψ 866:Ψ 847:− 837:∗ 833:Ψ 826:∇ 823:ℏ 817:− 811:Ψ 808:− 805:Ψ 799:∇ 796:ℏ 790:− 782:∗ 778:Ψ 567:frequency 263:ℏ 260:π 242:Φ 199:ℏ 196:π 178:Φ 163:CGS units 2076:30913579 2068:17753357 1788:(1931). 1700:See also 1625:kilogram 1619:and the 661:, where 473:and the 391:.8484... 158:SI units 2040:Science 2009:Bibcode 1974:Bibcode 1939:Bibcode 1802:Bibcode 1652:‍ 1182:gives: 633:complex 461:‍ 398:‍ 365:‍ 110:. Both 96:, i.e. 35:Please 2074:  2066:  2058:  1837:  1656:ampere 1617:second 1492:, the 1482:. 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Index

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magnetic flux
Aharonov–Bohm effect
superconductors
SI units
CGS units
Fritz London
Aharanov-Bohm effect
below
Wb
Hz
V
superconductor
superconductor
Planck constant
electron charge
Cooper pairs
Little–Parks effect
Fritz London
phenomenological model
Josephson effect
potential difference
frequency
conventional value
2019 revision of the SI
superconductor
minimal coupling
current density

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